Call at&t we have prepaid cell for our teenage sons. The At&t plan is called free to go. You have to get cards every 45 days to keep the phone active, but you don't lose your number like other plans and the cards come as cheap as $10.
The $100 for a year that was mentioned is trac-phone, for this you would have to purchase a new phone as their technology is imbedded in the hardware of the phone, you can also lose your number if you forget to get a new card before your expiration date. Hope this helps!
