I like Skype.  Say it with me..."I like Skype."  Now, I don't want to seem too much a pusher of Skype, but I have to say, I'm impressed with this business model (along with Netflix, they're the best 21st century biz models I've experienced.)  

Skype takes telephony and translates it into the digital future.  Start thinking of your computer as a telephone, is how I could best describe it - a very cheap telephone.  And they have business packages, which is why I'm throwing it in our Toolshed.  Mostly likely your office has one computer, quite possibly several.  With Skype you can make FREE computer-to-computer audio and video calls - and the quality is super sweet (I use it constantly for personal and business use on a Dell Inspiron 1525.)