You need to have credit to make any sort of calls. I have a nokia prepaid, which isn't too bad that we only paid $60 for. You can get them even cheaper. Some as low as $40 I'm sure.
If you have someone else with a prepaid, they can send credit to her phone, which can be as little as $1. Minimum you can usually get is $20, but you might be able to get $10 through some companies. Not sure.