How do eSIMS work?

Forums › New Zealand Mobile and Wireless › How do eSIMS work?

quickymart

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#324106 28-Feb-2026 08:28

I'm thinking of taking a holiday overseas and wondering how eSIMs work.

I have a plan with One (awful name) and have for years. However their roaming costs are gradually creeping up. In order to keep costs down, could I purchase one of those roaming eSIM deals I keep seeing online (Saily is one I see quite a bit) but keep my NZ number still running?

In tandem with this, could I route data over the roaming SIM, but keep the NZ SIM if someone calls or texts my NZ number?

Sorry if this sounds like a silly question but I haven't seen it covered here previously.

Jase2985

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#3465639 28-Feb-2026 08:39

They work the same as a regular sim, they just don't take up a physical sim slot, and you can download it from the provider to your phone without physically having to wait for something to arrive.

You can then store a number of them on your phone and toggle them on and off as needed. I've had 3 on mine at once when travelling.

If your phone supports multiple active SIM's you can do what you are proposing with having multiple SIMs active.

freitasm

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#3465642 28-Feb-2026 08:59

For those "travel" eSIM services you usually download their app and can use it to select plans, buy more data, etc.

Note that if you don't want to pay roaming you will have to turn off your NZ SIM/eSIM, which means you won't be able to make or receive calls on your NZ number.

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CYaBro

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#3465645 28-Feb-2026 09:25

freitasm:

For those "travel" eSIM services you usually download their app and can use it to select plans, buy more data, etc.

Note that if you don't want to pay roaming you will have to turn off your NZ SIM/eSIM, which means you won't be able to make or receive calls on your NZ number.

Unless you use wifi calling only.

One don’t charge you roaming fees for wifi calling overseas do they?

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DjShadow

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#3465646 28-Feb-2026 09:42

There is a trick to making your One NZ connection use WiFi calling over the travel sim, it does involve changing your network connection from Automatic to Manual so it won’t try to connect to an overseas carrier network

quickymart

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#3465666 28-Feb-2026 11:32

freitasm:

For those "travel" eSIM services you usually download their app and can use it to select plans, buy more data, etc.

Note that if you don't want to pay roaming you will have to turn off your NZ SIM/eSIM, which means you won't be able to make or receive calls on your NZ number.

That's what I was wondering about. So I'd still pay the roaming charges the second someone calls me on my NZ number.

I think I'll probably just get a data-only eSIM from the likes of Saily (do they even have a phone number assigned to them?) and use Whatsapp or Signal for all my communications instead of phone calls or SMS.

Jase2985

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#3465673 28-Feb-2026 12:32

Depends on your provider, if its one of those $8-10 dollar a day to use your NZ plan then i think as soon as it connects you get charged. if its like spark/skinny then you only get charged when you use a service, ie data/text/call.

Data only SIM's dont usually have a number assigned to them.

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richms

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#3465675 28-Feb-2026 12:52

They do have a number and when I tried one of the esim apps to see if it would work on a seldom used phone it added that number to my Google account and they then wanted to SMS it when. I logged in as it was then overseas looking and suspicious.

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freitasm

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#3465710 28-Feb-2026 18:03

@quickymart:

freitasm:

For those "travel" eSIM services you usually download their app and can use it to select plans, buy more data, etc.

Note that if you don't want to pay roaming you will have to turn off your NZ SIM/eSIM, which means you won't be able to make or receive calls on your NZ number.

That's what I was wondering about. So I'd still pay the roaming charges the second someone calls me on my NZ number.

I think I'll probably just get a data-only eSIM from the likes of Saily (do they even have a phone number assigned to them?) and use Whatsapp or Signal for all my communications instead of phone calls or SMS.

Or see the comment above about WiFi calling.

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Handle9

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#3465724 28-Feb-2026 19:53

freitasm:

Note that if you don't want to pay roaming you will have to turn off your NZ SIM/eSIM, which means you won't be able to make or receive calls on your NZ number.

Not necessarily. I disable roaming on the normal SIM card and only enable data to the travel sim. The normal card only functions as a phone/sms SIM card.

YMMV depending on the phone

trig42

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#3466134 3-Mar-2026 08:59

I used a Travel SIM last year through Asia (Hong Kong, Vietnam, Thailand, Indonesia, Singapore) and Australia.

Just turned off my OneNZ SIM, told people before I left to get me on WhatsApp. Worked perfectly.

I didn't try using my One SIM/Number - I suppose I could have set it up for WiFi Calling but I wasn't worried about receiving (mainly work) calls.

quickymart

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#3466153 3-Mar-2026 10:05

trig42:

I used a Travel SIM last year through Asia (Hong Kong, Vietnam, Thailand, Indonesia, Singapore) and Australia.

Just turned off my OneNZ SIM, told people before I left to get me on WhatsApp. Worked perfectly.

WhatsApp using your NZ number - is that right? With the data routed over the travel SIM?

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OldGeek

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#3466289 3-Mar-2026 12:03

To the OP: have a look at this topic:

https://www.geekzone.co.nz/forums.asp?forumId=11&topicId=323840

This gives an example where I was able to use a data-ony esim in Australia, avoiding roaming charges and also being able to receive calls from my NZ number, and make calls to Aistralian (and probably NZ) numbers.

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