I have a relative who is irresponsible but needs/wants a smart phone. No international travel, only domestic US, Southern California.

I'm thinking of getting her a GSM smart phone with a prepaid plan. I could go Straighttalk, but not sure if she can get TMO coverage where she is, which in my experience is spotty.

I could buy an AT&T sim from eBay and buy an unlocked phone, set up a pay plan with STraighttalk that I would pay for, and ship her the phone.

Any suggestions:

1. Which plan
2. Which phone, would like to spend less than $100 if possible

thanks