By Kimberly Koerth

**Editor’s Note: Which is America’s top wireless network? Click here to see what we discovered.**

AT&T‘s recently approved IP-network trials in two southern states are coming under fire from Sprint and T-Mobile, who say the trials are holding back the industry as a whole from developing cross-carrier IP interconnections.

“AT&T’s proposed experiment [in Alabama and Florida] is putting the cart before the horse,” Sprint wrote in a filing quoted by Wireless Week, saying that if carriers don’t migrate their wholesale and intercarrier interconnections to IP first, the benefits of a transition to an all-IP infrastructure will be lost.

Sprint added that the other carriers shouldn’t be forced to wait for the experiment to finish before interconnecting in IP format with other carriers or moving from their legacy networks to all-IP.

In a separate filing, T-Mobile said trials such as these shouldn’t be allowed to distract from ensuring interconnecting among all carriers and shouldn’t involve “unnecessary” or “inefficient” TD-IP conversions or points of interconnection.

AT&T expects to see large cost savings by shutting down its legacy networks. The carrier has committed to phasing out copper in favor of an all-IP infrastructure by 2020.