Thanks for all the comments.
1. TMO's wifi [UMA] does not work on apple iPhones - i offered her my old BB which has UMA but she declined
2. She wants a larger screen so traditional non-smart phone won't do - again,i have older samsung with UMA call feature that would work, but she declined!
3. Prepaids are not economical - plus I don't think you can't port existing number to prepaid
So we're debating whether to switch her over to Verizon, get a new iPhone 4s or to wait for new iPhone later this summer before making the switch. Regardless, her mobile phone bill is going to get a huge spike when we make the move!