global verizon phones to straight talk

ok i currently have lg optimus g (att) on straight talk. i like my phone but i would like better battery life. botht the motorola razr hd and the motorola droid ulta support 3g HSDPA 850 / 900 / 1900 / 2100. now i dont care about 4g because i dont need it. so will this work. and if it does will it use T-Mobile or att. i need att coverage. i dont think i am going to activate it as a verizon because i believe straight talk does not support it. my top goal is att coverage that i cant part with.

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I'm not sure if those phones have the GSM restrictions on them or not. I know the droid razr did and would not work on any US GSM networks.