What Kind of iPhone is This?

hello,
have white iphone 4s 16gb unlocked (so thought).
bought phone $649 on craigslist. before guys bash me using craigslist, here me out: realize mistake in using , have learned lesson.

bought thinking able use t-mobile sim card it.
got home, opened box, put sim in, , phone went through "apple splash screen" , told me set phone.

***the phone gave signal of 1 (one) bar, , on edge. yet never said "t-mobile"***

going until told me @ end sim card not valid , insert sim card carrier whom bought from. not knowing do, inserted old at&t sim (currently has no service on whatsoever) , phone got past set-up screens.

clueless, went settings --> general --> , looked @ model number. reads "md237ll." carrier "at&t 11.0." suspected because had at&t sim inserted.

decided take out at&t sim , insert t-mobile. phone went through "apple splash screen" once again , ended last time: 1 bar, edge network, sim not register.

once again inserted at&t sim , got through home screen. however, time turned on airplane mode , took out at&t sim. inserted t-mobile sim , turned off airplane mode.
sure enough, phone registered t-mobile's network. told me had 1 new voicemail. there 0 (0) signal bars. went settings --> general --> , carrier "carrier 11.0." yet phone connected edge said. wifi off.
test this, tried making phone call: call not go through. tried siri , sure enough, siri worked.

stuck. do? i've restored phone factory settings via itunes. yet still happens.
please me.
thanks!

 

sell , buy unlocked phone apple (which should've done in first place).
can't unlock phone, you're screwed if keep it.

 

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