Useful websites

http://www.voip-info.org
A wiki website where anybody can add notes to the website about anything to do with VoIP. As a result the various contributions made have turned this site into a near complete source of all industry news, a service provider directory and a manual for lots of the software and systems.

http://www.itspa.org.uk/
The website for the UK Trade Association for Internet Telephony Service Providers.

http://www.sineapps.com/
A website dedicated to Voip service and Asterisk.

http://www.ofcom.org.uk/media/mofaq/telecoms/voip_faq/

The VoIP pages from the UK Communications regulator, OFCOM.

http://www.fcc.gov/voip/
A US government site that is an excellent VoIP resource.

http://en.wikipedia.org/wiki/VoIP
Wikipedia's comprehensive pages on VoIP