Yahoo Voice has launched today (March 22, 2006) which gives users full inbound and outbound Voice Over IP or VOIP telephone calling capabilities. The product will directly compete with Skype which was gobbled up by eBay in 2005. Yahoo Voice should help squander the near domination in the space by Skype, though other services like Gizmo do exist.
Yahoo requires users to download the latest version of Yahoo Instant Messenger client and will compete by offering slightly cheaper service than Skype at $2.99 a month or $29.90 a year and then two cents a minute to place calls.
I am not a big Skype user since I pay for Vonage, another VOIP service that requires a little more hardware and setup than the PC based services. However, if I was not using Vonage, I am sure I would be using one of the other PC based VOIP options.
To better understand how Yahoo Voice works be sure to check out the How To Make Phone Calls Page. Also check out these reviews on TechCrunch and PC Magazine.