Skype

Skype is currently the 800-pound gorilla in the softphone business. With compatible clients for Mac, PC and Pocket PC, access to broadband is the primary limiting factor in placing a Skype call. Computer-to-computer calls are free, with additional fees for placing calls to landline and cellular phones. Voicemail currently costs extra. A headset or microphone and speaker combination is required for communication, which makes this a little clunky for replacing the traditional phone, although several decent USB phones offer a reasonable alternative. A new beta service is working toward the concept of traditional telephone numbers linked to a Skype account. Network call quality varies greatly with latency issues worse than what's familiar to cell phone callers and echo that can be hard to troubleshoot. A massive user base makes this an interesting option for free international calling. Skype's biggest disadvantage is incompatibility with other software VoIP services.