Scope of setup instructions
Before I go any further, I'll state clearly that I'm not trying to document how to configure the SPA3102 for anything other than the purpose which I use it for. I imagine that my configuration is quite similar in most respects to other potential UK users and this is my main motive for writing this series of pages. In practice other people will have different requirements and I can't hope to document everything.
By nature I would try to document everything. If the difficulties I had are anything to go by, even where I can see how to achieve something, I'll refrain from saying. This is simply because the potential for underlying problems is so great that I don't want to venture what I don't know for sure. In addition, the nature of my particular setup is sufficiently complex that I'd rather not risk experimentation to find out. Especially so, now that it actually works!
The setup that I achieved, makes use of my existing ADSL combined modem/router. The SPA3102 is attached to my loacal area network, and the SIP messages traverse the NAT (network address translation) of the router. I think I am only able to do this because I have a static IP address with my ISP.
Although it is nice to be able to make VoIP calls for free I already have Skype hardware. What I really wanted was a cheap second phone line with Voicemail, incoming Fax capability and the possibility of a United States incoming number for free. I wanted to be able to dial out through either telephone number or Skype, and receive calls from any source, with a single phone handset. The unit does all of this (except the skype part), and I am aware that it has additional routing capability should I need it.