I have just joined with compass and am on the mammoth plan. I got the text to say that my service has been connected but i hit a snag when trying to configure the router i had from my last ISP Vodafone it's an EchoLife HG556a HW.C.
The default user setup page (i.e. 192.168.1.1 > username: vodafone, password: vodafone) did not show any information about the VPI/VCI values etc the only relevant input fields available were those for the Vodafone Account Username and Password (PPP U/N & P/W).
I had to get into my modems admin/advanced setup page which was a whole other mission in and of itself; it wasn't admin/admin, I google searched and found a url to put in, that allowed me to save my modems backup settings config, I got the admin password from this file after a little digging.
Once in i found that the compass settings were already there by default i.e. VPI:0, VCI:100, VC/MUX.

So my current WAN interface is as follows.

VPI: 0
VCI: 100
*Service Category: UBR Without PCR
Protocol: PPPoA
Encapsulation:VC/MUX
PPP Username: xxxxxx@mammoth.compassnet.co.nz
PPP Password: xxxxxxxxxxxxxx
PPP's MTU: 1492
*PPP's LCP Echo-req Interval: 30(sec)
Authentication Method: AUTO

The two lines with asterisks(*) I have no idea what they do but i left them as they were.

In the modems diagnostics tool it says the following:

Local NetworkTest
LAN(1-4): Pass
Test your Wireless Connection: Pass

Connection to DSL service provider
Test ATM OAM F5 segment ping: Pass
Test ATM OAM F5 end-to-end ping: Pass

Connection to Internet service provider
Test PPP server session: Fail
Test authentication with ISP: Pass
Test the assigned IP address: Fail
Ping Defauly Gateway: Fail
Ping primary Domain Name Server: Pass

Screen shots of various dsl and disgnostic windows - imgur.com/a/cJVJN

(As a side note i also tried a D-Link modem that didn't work either, but in its status page it said i was connected to the exchange just not the internet.)

At this point I rang compass and they couldn't tell me anything new (I had their configuration settings from the Compass website i.e. VPI/VCI/Encapsulation). So upon failing to connect me, their advise was to ring my modems manufacturer (Huawei) and get them to configure my modem to Compass settings, who after a lengthy walk through put it down to being up to compass are the only ones that can sort it.

After ringing compass a second time they told me to ring Vodafone to ask them how to unlock my modem because they apparently hard code something into the modems so they will not work with other ISPs. To this Vodafone informed me that my modem model is open, they do not put anything onto them that would require them to be unlocked and should work with any ISP.

...At an extra $75 I have reluctantly ordered one of Compass's pre-configured routers, but as it's friday, I won't see it til next mid-week and i still have time to cancel it so...If any savvy person out there could help me get connected you'd also be saving me 75 bucks!