That's why all you guys need SKYPE!!! Free, and it works. If the person is online, call... if not... don't, cause they wont answer.
If I'm on my computer, I tend to leave it open... heck... Even if I'm not on it, at least I can see who tried to call that I did not answer...
Skype is the way to go.
Regular phone calls are fine if you know the person who you are calling basic schedule... other than that it's very hit or miss.