This card has the benefit that you can connect an analogue phone as an extension, and supports UK caller id in the main Asterisk source without any patches.  More ...

 
The basic configuration I described will work successfully; however, there are a number of features that you may want to enable. For example, accepting incoming faxes to email, and automatic sending of voicemail messages by email.  More ...

Is a very impressive software system for making a phone switchboard. The core software is Asterisk, which can be installed under various forms of Unix, including Linux and MacOS X. It supports the SIP protocol for network phones, various Digium cards for analogue phone line and analogue phones, and understands VoIP.  More ...