I have a trac phone. Yes, I'm a cell phone resister! I have to be on the phone all day for work, and just don't get all that excited about having a cell so that people can reach me ALL the time, ha! But I do like having it just in case, and it's cheap.
So it's not fantastic (I say that as a person who's never had another cell phone), but I do think it's fine for emergencies. You can add time by buying cards from the pharmacy. For some reason, it won't let me make calls to a friend of mine who has a Verizon cell phone (it goes straight to his vm, and his calls to me from his cell to my trac go straight to my vm).
I've had times when it's been difficult to hear what the person is saying, esp if I'm indoors, or if there's alot of noise around me (like traffic).