Lessons learnt: setting up a retro phone display in the office using SIP/VoIP

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ZL2DanF

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#324644 7-May-2026 15:55

Hi GZ,

I thought I would share a recent win with the Geekzone crowd. I am fully aware I am no expert and realise this was achieved by, figuratively speaking, standing on the shoulders of experts — including a few helpful people from this community (Thank you, again! :-) ). Hopefully it is of some interest, given this is a forum full of people who enjoy tech, and tech related rabbit holes.

My day-to-day work is in telco. I am Wellington-based and quickly approaching the two-decade mark in the industry. These days, I am predominantly office-bound. While chained to the desk, I have got to know one of the draftsmen who sits across from me.

Let’s just say this guy has been on the job for a little over twice as long as I have been alive.

He has a small collection of retro phones on display, including a PERT, a Statesman, a couple of 100-types, some 1956/57-era Bakelite phones, and even an Ericofon/Cobra.

One day, I said to him in passing:

“Would you like those phones to ring again someday?”

I swear his eyes lit up. The answer was a very enthusiastic “yes”.

Originally, I brought the phones back to life using an old Panasonic KX-TES824 PABX and a few three-wire plug-in adaptors. That worked well enough until last week, when the Panasonic finally died.

It is currently in bits on the dinner table — one of the very few (dear I say) perks of single life. The ex would almost certainly have had something to say by now about the parts, tools, and gear all over the place.

I have made some progress with the Panasonic. I have got power back, but I suspect there may be a memory, backup CMOS, or EPROM-related issue. After a couple of resets the config can be reloaded and it works okay until it is powered off. When it is powered back up, the master phone starts flashing and playing Minuet, which cant be a good sign.

Anyway, while I am still mucking around with that, I ended up putting together a “Mark 2” version, where the switching has effectively been collapsed onto IP/SIP. For any NEAX 61 S/K/M/E people here, I suppose I have basically recreated a glorified RLU.

What I can say is that it was far more of a headache/drama than expected to get everything working properly. Tones, ringing, codecs, pulse dialling and a bit of good old-fashioned trial and error. I would be lying if I said there was not a lot of advice from Uncle and Aunty Google & AI too.

However, it all seems to work okay now. The phones, whether DTMF or pulse dialling, all work and ring properly. All Done in my own time, but I (somehow) stuck at it, and surprisingly it was achievable with affordable off-the-shelf gear.

I have also shared a version of this write-up on the Facebook group Ex NZ Post Office Construction Staff, and I have been in touch with the good folks at Ferrymead. Feedback so far has been positive.

There are bound to be a few others here with telephone collections and/or similar projects, so I am happy to share lessons learnt, config files, or setup notes where useful. I am also very open to suggestions and improvements. Feel free to reach out,

I reckon next step get some outside lines/SIP trunks into this beast!

Now what takes the cake…A couple of the office inmates are not fans of the “loud” ringing bells. Let's just say, I am in no rush to adjust the ring power setting 🤣

Cheers,
DanF

High Level Detail….

Ringtone c=400/200-400/2000
Ring Frequency: 25Hz
Dial Tone: f1=400@-9,c=0/0
Engaged Tone: f1=400@-9,c=500/500
NU Tone: f1=400@-9,c=250/250;

Basic Block Diagram…

HT818 8Port ATA (In office/remote location)<<<>>>MikroTik hAP ac (connected to guest wifi) <<<>>>Internet<<<>>>My Home Router<<<>>>Traffic to sip server-(currently Raspberry Pi)

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#3488503 7-May-2026 16:40

Very nifty!

richms

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#3488504 7-May-2026 16:40

Oh no, I have a panasonic I got a while back to do the same thing with, hope this isnt a known problem with them.

I also have an 8 port linksys ATA if the panasonic failes me.

Richard rich.ms

SirHumphreyAppleby

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#3488511 7-May-2026 17:13

I have a phone from the 1930s IIRC. Can't dial on it, but it would be great to bring that back to life.

It's one of those things that is unlikely to ever happen, but I will hang it on the wall at some point.

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#3488512 7-May-2026 17:20

I was thinking of finding a door phone for the Panasonic to use it as a doorbell, but I would miss things when I was not at home. No need for outgoing dialing for that and having an old candlestick or wall phone as a door intercom would be peak weird.

Richard rich.ms

nztim

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#3488524 7-May-2026 18:54

There are some SIP ata adapters out there that support pulse dialing, what is going to be hard is finding ones that support the NZ reverse dial pattern

Thats where rotatone comes in....

https://oldphoneworks.com/products/rotatone-pulse-to-tone-converter

This converts the rotary pulses to touch tones, and even supports the NZ Dialing pattern, just select NZ dialing form the drop-down list while ordering

They even have instructions for wiring into the 746 (Marketed in NZ as type 100)

https://cdn.shopify.com/s/files/1/0654/8704/4831/t/3/assets/description_image_Rotatone_GPO746.pdf?v=1657588945

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ZL2DanF

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#3488635 8-May-2026 10:39

Cheers, Tim — that is useful info, and I appreciate the links.

Rotatone looks like a good, non-offensive and non-intrusive option, especially given the “unique” NZ reverse dial pattern. On a side note — and potentially another can of worms — I would love to get to the bottom of why NZ went down that particular dialling path in the first place. There seem to be a few theories and urban legends floating around. No doubt that is a story, and possibly a debate, for another thread. 😅

Cheers for the circuit diagram too. It reminds me of another situation where I opened up a Type 100/101 phone and found a paper clip shorting out a couple of pins, which I assume was someone’s attempt to “convert” it to two-wire operation (not stupid if it works, i suppose)

My preference, probably out of stubbornness as much as anything, is to keep the phones as original as possible unless I absolutely have to modify them. Part of the fun (well, for me anyway) is trying to make the old gear work as close to “as-is” as practical.

So far, the Grandstream HT818 has actually been surprisingly capable once the settings were dialled in. With 25Hz ringing, NZ-style tones, and pulse dialling, it appears to be behaving well enough for the current office jack-up. A bit of mucking around, but it is doing the job and have avoided to alter the phones themselves - always, mindful of and try to re-risk and not breaking other peoples gear/pride and joys.

That said, I will definitely keep Rotatone in mind, looks like a quick and clean option – Won't be a showstopper to find out what the Kiwi to Canadian dollar is :-)

Cheers,
DanF

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nztim

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#3488876 8-May-2026 17:25

ZL2DanF:

I would love to get to the bottom of why NZ went down that particular dialling path in the first place.

it's because we decided to use 111 as our emergency number instead of 999 as a result 3 clicks from electric fences made false emergency calls

Why we decide to use 111 instead of 999 or 000 is beyond me and I don't have the answer to that

ZL2DanF:

My preference, probably out of stubbornness as much as anything, is to keep the phones as original as possible unless I absolutely have to modify them. Part of the fun (well, for me anyway) is trying to make the old gear work as close to “as-is” as practical.

So far, the Grandstream HT818 has actually been surprisingly capable once the settings were dialled in. With 25Hz ringing, NZ-style tones, and pulse dialling, it appears to be behaving well enough for the current office jack-up. A bit of mucking around, but it is doing the job and have avoided to alter the phones themselves - always, mindful of and try to re-risk and not breaking other peoples gear/pride and joys.

Does the HT818 support NZ reverse dialing? or is a 9 a 1 etc etc

Rotatone has other advantages too, like been able to dial a * or # and have redial and from an exterior perspective the phone looks the same, you just hide it in the case

Any views expressed on these forums are my own and don't necessarily reflect those of my employer.

MadEngineer

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#3488879 8-May-2026 18:33

Many extended smoko breaks and Arcoroc cups must have been used in the making of that. Does someone there also drive an L300, by chance?

IYKYK

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ZL2DanF

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#3489191 9-May-2026 14:03

nztim:

it's because we decided to use 111 as our emergency number instead of 999 as a result 3 clicks from electric fences made false emergency calls

Ive never heard the yarn about electric fences before – But, it is plausible... I should know better, hours and hours spent in years gone by chasing electric fence ingress on pcm system faults as well as choking pairs etc – The ones I have heard are false calls from 40 & 70lb open wire lines tapping in the wind, and damp/soggy paper insulated pairs arcing.

I understand 100, 150, 200lb wire was also historically used, but well before my time. Reminds me I still have my Nicopress tools and Line-Vice/Strainers :-)

The whole 111 instead of 999 or 000…Hopefully, just another case of simplest explanation usually being the correct one where kiwis just went off to do their own thing.

The other mystery in NZ Telco – What does RLG stand for? Theres a few theories out there depending on who you talk to. But, we all know it’s a pilar/dp/copper loop – A topic maybe for another time? 😅

nztim:

Does the HT818 support NZ reverse dialing? or is a 9 a 1 etc etc

Seems to – Have temporarily changed 2x extension to 4009 & 4001 – So far so good!

MadEngineer:

Many extended smoko breaks and Arcoroc cups must have been used in the making of that. Does someone there also drive an L300, by chance?

IYKYK

No comment on the Smoko breaks 😂…However, I do recall the in my early days, one of the tech’s I was working with stating “Morning smoko is right, Afternoon smokeo is a privilege” – Probably more to the story on that one…Sounds like something resulting from a historic clash between the Post Office Union & Management of the day. 😅

…and the ubiquitous and pretty much unbreakable Arcoroc cups (I have seen one bounce off a concrete floor once!)….they still seem to be everywhere throughout the land, almost part of the fabric of our pokey little society – I saw some of these mugs on sale in Briscoes recently and picked myself up half a dozen. Although wouldn’t surprise me if a few of our fellow Kiwis would be shocked to learn they are of French extraction...

Don’t get me started about the L300s – I progressed through 2x of them before moving through a couple of Hyundai iLoads then later Mitsi Utes.

I will say, the diesel non-turbo long wheelbase version was a bucket of bolts. However, my first van was the short wheelbase petrol version. It had no trouble getting off the line…But who here can say they don't remember their “first” 🤣

Technofreak

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#3489287 9-May-2026 20:54

nztim:

ZL2DanF:

I would love to get to the bottom of why NZ went down that particular dialling path in the first place.

it's because we decided to use 111 as our emergency number instead of 999 as a result 3 clicks from electric fences made false emergency calls

Not quite correct. New Zealand chose the reverse dial pattern for a variety of reasons.

A quick google seach came up with this.

Unlike in many other countries, the numbers on New Zealand rotary phones were arranged in a reversed order so that the numbers printed on the dial would appear in the correct sequence when dialed. This design was influenced by New Zealand's existing telephone number plan at the time rotary exchanges were installed. It was also related to considerations about wear on the dial mechanism, with the reversed mapping calculated to reduce wear issues. Essentially, the reverse dial was a unique adaptation to fit New Zealand's specific telephone system requirements and to optimize the durability of the rotary dial.

Because of this choice, 111 was chosen for calling emergency services. The reason being not because of electric fence interference but because the telephone lines were composed of two bare copper overhead wires, at least for part of the way between the exchange and the house.

If these lines got too much slack in them they could bump together in the wind and make and break the circuit back to the exchange thus simulating dial pulses. It was easy to simulate three single separate pulses which dialed 999 but very hard to get three lots of sequential 9 pulses to simulate 111.

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Technofreak

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#3489290 9-May-2026 20:59

I have planned something like you"ve done for a while. In fact my plan had it's origins back in the 1990's when I finished at Telecom.

I have a collection of old telephones and not so old dial and decadic pulse phones including two coin box phones.

I intend to hook them all up one day soon to the 20 line 100 type PABX I have stored away.

It will be an interesting project when I get time and space to set it up.

The Ring and Tone relay set in the 100 type means no need to have to modify somthing to get the correct ringing and tones.

I might have one or two old DTMF phones lying aroound as well and if I dig through the stuff I have I may even find a DTMF to decadic pluse convertor to make them work too.

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#3489305 10-May-2026 08:12

"Essentially, the reverse dial was a unique adaptation to fit New Zealand's specific telephone system " Not quite unique, the Oslo region in Norway used the same dial.

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#3489307 10-May-2026 09:19

ZL2DanF:

I would love to get to the bottom of why NZ went down that particular dialling path in the first place. There seem to be a few theories and urban legends floating around. No doubt that is a story, and possibly a debate, for another thread. 😅

The story I heard was that it was a simple Non-Tariff Trade Barrier.

The NZ market was unique and by world standards very small, so the Plessey factory (in Porirua?) was able to enjoy an expensive monopoly in making NZ telephone handsets. The reverse dialing plan made it uneconomic for overseas high volume plants to compete.
Or so I heard

Technofreak

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#3489308 10-May-2026 09:37

PolicyGuy:

ZL2DanF:

I would love to get to the bottom of why NZ went down that particular dialling path in the first place. There seem to be a few theories and urban legends floating around. No doubt that is a story, and possibly a debate, for another thread. 😅

The story I heard was that it was a simple Non-Tariff Trade Barrier.

The NZ market was unique and by world standards very small, so the Plessey factory (in Porirua?) was able to enjoy an expensive monopoly in making NZ telephone handsets. The reverse dialing plan made it uneconomic for overseas high volume plants to compete.
Or so I heard

OWT (Old Wives Tale). It was an engineering decision made by the NZPO.

While Plessey made phones here I'm pretty sure the decision to use the reverse dial predates local manufacture of what were BPO phones.

As it was the only difference was the dial plate which was numbered backwards. All other dial and phone components were the same as the BPO ones. Hardly a barrier to another manufacturer.

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#3489316 10-May-2026 11:50

I saw your post on Facebook, thought I might eventually find you here.

Kudos to you for having the patience!

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