T-Mobile US has won a declaratory ruling that could force AT&T and Verizon Wireless to charge lower prices for data roaming. T-Mobile argued in a petition to the Federal Communications Commission that the biggest carriers charge their smaller competitors artificially high prices. The petition asked the commission to offer specific guidance and enforcement criteria for determining whether any given data roaming agreement is commercially reasonable. The FCC granted T-Mobile’s request today, rejecting arguments made by AT&T and Verizon.