That's because in the future operators may transmit voice calls using VOIP over LTE, classifying voice as a data service. Without data roaming, an operator might lose the ability to let its customers use voice services when outside of the operator's coverage area.

The rule proposes to allow operators to negotiate and determine terms on a customer-by-customer basis.

Genachowski sent the letter to 12 members of Congress including Republicans Representative Joe Barton of Texas, Representative Marsha Blackburn of Tennessee and California Representative Mary Bono Mack.

The IDG News Service