Here are some useful articles from around the web.
A nice article our pals from across that pond at BBC News. It focuses mainly on Skype and Vonage. Some interesting comments by real life impartial VOIP users at the end of the article. [Read Article]
BBC News - Making phone calls over the internet
Another article from BBC News about using Skype and Vonage. Reports on how internet phone are set to take on land lines. [Read Article]
VOIP-Info website - The Voip mega site
A monster site for all things VOIP. A Wiki covers everything related to VOIP, software, hardware, service providers, reviews, configurations, standards, tips & tricks and everything else related to voice over IP networks, IP telephony and Internet Telephony. [Visit Site] The also have a nice Intro. section here