Just don't go too far away from the city straight talk uses Sprint (no roaming)
You cant just say they just use sprint... If I recall correctly -- it's just Android phones purchased from them that use sprint. See coverage map -- »www.straighttalk.com/Coverage
You can buy SIM cards from them for use in AT&T or T-Mobile devices.
Most Android phones from them are Sprint, but there's T-Mobile ones, and a phone with AT&T, and a phone with Verizon (no roaming on VZ). Then they have ST SIM, which you can choose T-Mobile or AT&T.
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