[BROOKNAM]

Maybe someone can give me a little clarification on the sim unlocker function, in the sub-level of the building i work at, verizon and sprint(cdma) gets spotty to no radio signal, while att and tmobile(gsm) works through out the sub-level. if i do the sim unlocker would i be able to switch to a gsm signal with the same sprint sim card? or would i be required to use a (gsm) sim card? also would this switch accure automatically or is it something that has to be manuely done?