With the new Yahoo Messenger 7.5, your friends and family members worldwide can call your computer from any conventional landline or mobile phone (Yahoo Phone In). You can also call any phone number from your PC via Yahoo IM client (Yahoo Phone Out)
Yahoo! subscribers get a personal phone number (with any city area code) for receiving incoming calls to their PC from regular phone lines and mobile phones. So even if you are located in New York city, you can still choose a number with San Francisco area code.
Yahoo! Messenger PC-to-PC calls remain free and there are a couple of other interesting free enhancements to these services, including a new Contact Search Bar within the interface and free voicemail (for both PC-to-PC calls and Phone In calls).
MSN is also testing a PC-to-phone service. AOL says it will have PC-to-phone calling available later this year. All IM services like Yahoo, Skype, AIM, MSN Messenger and Google Talk offer PC-to-PC VoIP calls for free.
Download Yahoo Messenger 7.5 with Voice (for PC-To-Phone and Phone-To-PC calls)
Download Yahoo Messenger 7.0 (for free PC-to-PC phone calls)
Yahoo! Voice Call Rates | Yahoo Phone Card
Sources: PC Magazine | Yahoo! targets eBay Skype | Om Malik's Screenshot