Voxcall enables VoIP on Facebook
Voxcall lets you click to call Facebook buddies, as well as field calls from them, as long as you both have a SIP URI (that's a VoIP address that acts like a phone number and looks like an e-mail address). Of course, if you don't have a SIP URI, you can enroll in the Voxcall Premium service, which supports placing calls to ordinary telephone numbers. And if you're worried about abuse or phone spam, as many click-to-call users are, Voxcall has implemented a PIN code verification which will stop malicious users from registering your SIP URI without your permission. The way it works, once you register, Voxcall places a VoIP call to your URI--and then you enter your PIN code.