BT VideoPhone1000 - will it work with other SIP providers?

The BT VideoPhone1000 is now down to £39.99 from BT, £69.99 for a pair and its even cheaper elsewhere. Its supposed to be used with BT's servers and they charge per mintue for calls, etc. I wondered whether it is possible to get it working with other VoIP providers including my own Askozia PBX.

From a little bit of reading of this thread I have discovered that the phone is a standards compliant SIP phone but it has the sip gateway address hardcoded and in the later firmwares the phone must make a connection to a BT HTTPS server otherwise the phone stops working.

If you have firmware 0.5.3.96 there is a way forward (just be sure not to connect it to the internet until you've read the rest), if you have another firmware unfortunately there is no way forward at the moment but Nosilla99 on the Scream forums is working on a possible solution.

The phone automatically connects to a server to download new firmware so if you have a phone with firmware version 0.5.3.96 there are two things that you must do (don't connect the phone to the internet before you've done this!):

1) Block the phone from updating its firmware from www.videophone1000.bt.com (you'll need to run a DNS server and make sure that that address does not get through to bt.com)
2) Re-route the address that the phone tries to connect to BT's SIP servers at sip.btsip.bt.net so that it is actually routed to your PBX, or SIP service (using your DNS server).

I have set my Monowall router up as a DNS forwarder which publishes itself as the DNS when it dishes out DHCP. I've then set it to override the DNS responses for those two addresses. This seems to be working fine when I do an NSlookup test.

All of this information came from Nosilla99 at the www.the-scream.co.uk/forums.