True - which is why you would buy the specified phone for that network. Once you receive the phone (i'm referring to the gsm models with a sim) you activate it on straight talk, then you can put that sim in your phone. ie; activate an E71 on straight talk, take the sim out, put it in an iphone...

Yes - you need to get a phone from straighttalk with the correct sim. Meaning certain phones they sell work on each of the networks, some on the at&t, some on the verizon and some on sprint. This is determined by the phone you purchase. So if you have an att iphone purchase a refurbished...