im pretty sure it can. straight talk is walmart. im using family mobile which is also walmart. i looked at the site and they have a phone similar to it. the one on the site is the samsung T401G. the feautures are the same its just the look is slightly different.
Can I use it instantly after popping in a SIM card? No need to buy prepaid cards if you've already purchased talking/texting credit or whatnot directly from T-mobile?
sounds like that would work. i dont see why not. the prepaid card is just a form of paying. if you can pay another way and have a sims card sounds good.