http://www.skype.com
I tried Skype briefly a while back and it was okay, but wasn't really any different than ICQ except for the voice chat, but they have some KICK ASS new BETA features.
You can get buy a phone # for SkypeIN, where people can call you on your PC ($30.00EU for 1 year of service, Includes a Voicemail Box for 1 year)
And get SkypeOUT, and call people on their phones $10.00EU blocks of time at a rate approx. of $.02/cpm.
The way I see it, I am usually on my PC or at least near it. If I am not, I usually have my laptop with me, and am near an internet hotspot. Using these new Skype features, it would be rare that I would need my cellphone for anything, other than emergencies, or for times when I'm not near a connection (rare occasion).
I just wanted to share with the class.
Enjoy!