Hi Is there a tablet 7-10" of size that will work with at&t/t-mobile or any sim card if i have unlimited data plan from them.so i can browse even if im on the road. i found huawei s7 and dell steak 7. are they unlocked,???are there any others?? can any sim card be used in these?? my budget is under $300. please help and recommend a good tablet that can work wity my current phone sim card. much appreciated.