... standby Apphone, Backcover of iphone 4 & 4s, supports two sim cards(WCDMA & GSM), GPRS, MMS with Large back up battery ... . Functions:Backcover of iphone 4&4s, protection,fashion,multifunctionsupports two sim cards(WCDMA & GSM), GPRS, MMSLarge back up battery capacity, ... ctn:5238g backup power case/extra power/external battery/ dual sim dual standby/ double sim extra charger for iphone4 & 4s / APPhone