I want to get a cellular iPad Air. Depending on what I hear about T-Mobiles's service will determine which carrier I go with. All of you folks who use/used T-Mobile give me the spill, how is the 4G speed?etc. I know the speed generally relies on good coverage. How reliable are connections? Can you roam around outside of the city and get good 4G? And any other thought that you have! Anything! Thank you all.