The classical VoIP service where you install a softphone client and make calls through your computer has its limits when it comes to making calls instantly. Say you are in a Facebook chat and someone you want to contact uses a service other than yours - like you using Skype and they using Google Talk. Talking to each other instantly would not be possible unless one of you signs up with the other's service.
With services like FriendCaller, talking instantly in such situations can be possible. Simply clicking on someone's Call Me link starts a conversation even if one of the talking parties is not a registered user of the service. Besides, FriendCaller is browser-based, which means there is no need for installing any application. FriendCaller also has interesting international call rates. Read more