I recently tried a program called Skype and am very impressed.
Skype allows you to phone other Skype users using your PC. The audio quality is excellent, and the echo control works very well (hands free speakerphone functionality.) The program takes 2 minutes to set up, and works through firewalls. There are other VOIP (Voice Over Internet Protocol) programs out there, but most (actually I think all) require you to reconfigure your firewall -- Skype doesn't.
Skype is free, and the version that I downloaded (126.96.36.199) does not include any adware. The program was developed by the team that built Kaza (which I don't recommend).
To use Skype you need a PC with a broadband internet connection, speakers, and a microphone or headset. It actually worked OK with the mic that's built into my notebook computer.
If you regularly approach the minutes limit on your cell phone, and don't have a land line (or want to save on long distance prices) try it. www.skype.com
I don't have any affiliation with this company.