I've just picked up a Cisco 7940G and configured it with SIP firmware (8.2). I'd like to use this as my office phone, communicating with POTS/PSTN via a Linksys SPA 3102 VoIP gateway.
In theory, this should be possible but I've been struggling with it for weeks now!
There's stacks of advice on the 'net but most of it assumes I'm running an IP PBX (like Asterisk) or using an external VoIP provider. I'll probably extend the system to do those things later but for now I just want the IP phone to ring when the PSTN rings and to be able to make calls on the PSTN using the IP phone. I have the admin guide for the SPA but it's about as clear as mud.
(Extra details: SPA is behind a NAT router and is configured in bridge mode. Plugging an analogue phone into the SPA works fine – it's just the IP phone bit that I'm struggling with.)