dual sim is a cell phone cover that hold 2 sim card. i have this, i have t-mobile and philippine simcard "globe" that roaming here in the u.s. i put this 2 sim card in one cell phone by using the dual sim cover. it depend to the model of your phone some of them come with back cover some are not. this is easy to use, let say you have t-mobile and cingular and your currently using t-mobile and want to go to cingular, all you have to do is press *3370# and the phone will shout off by itself and turn on by itself and now your in cingular network. do this again and it will bring you back to t-mobile network. i get this to ebay and look for a seller name JECKRESE. hope this info will help you. take care now.
