The two leading wireless carriers in the United States built up huge smartphone user bases while luring customers in with unlimited data plans. The writing was on the wall years ago, however, and as mobile data usage exploded, Verizon Wireless and ATT both dumped their unlimited plans in favor of tiered data offerings that slam users with overage charges if they use too much data in a billing period. Sprint and T-Mobile continue to use unlimited data plans as a point of differentiation with their larger rivals but as one analysis pointed out this week, the days of unlimited data at Sprint and T-Mobile are numbered. Writing at PCMag, longtime wireless industry reporter Sascha Segan has penned a piece that