reply to Biscuit1001
Re: Structural Issues Straight Talk uses major networks' towers. Depends where you are in the country, you could be on ATT or Verizon's towers. Also, you can purchase just the SIM and use it in your own unlocked phone, ATT or Verizon's phone as well without having to root your smartphone to custom ROM like some of the other prepaid carriers will make you do if you are using your own smart phones. Really, no comparison IMHO..
my straight talk phone uses Sprint. As I noted above, they use all carriers that own their own networks, TMO, ATT, VZ and Sprint. It just depends on the area you purchase your phone and the phone.
reply to EasyBob
There is one phone that will work on Verizon. And obviously, a given phone can't switch back and forth, but they have SIM cards and several phones that run on AT&T. AT&T includes roaming partners, Verizon doesn't. They seem to default to Sprint, probably because Sprint is very MVNO-friendly, and charges cheaper rates for their crappy network.