AT&T is warning the FCC it may have to wait until it has voice-over-LTE (VoLTE) fully deployed to begin offering voice roaming to CDMA operators over its 700MHz spectrum.

Joseph Marx, assistant vice president of AT&T Inc. (NYSE: T)'s services division, clarified comments made on a conference call last week in a note to the Federal Communications Commission (FCC) 's Wireless Telecommunications Bureau. He was specifically addressing a statement AT&T made that "it may be necessary for some operators to wait until Voice over LTE (VoLTE) roaming is available before operationalizing LTE data roaming."

Marx writes:

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AT&T currently has VoLTE deployed in parts of about 20 states and is working toward a nationwide footprint to match both Verizon Wireless and T-Mobile US Inc. , but hasn't put a timeline on its deployments yet. It has said it's also working with Verizon to achieve interoperability between one another's VoLTE services this year as well. (See AT&T Promises More VoLTE Markets in 2015 and Verizon, AT&T Plan VoLTE Harmony in 2015.)

AT&T has been working toward interoperability with other smaller carriers in the US as well, following a pledge in September 2013 to resolve compatibility issues between band 17 and band 12 in the 700MHz spectrum. (See AT&T Inks First LTE Roaming Deal in Canada and Mobile Migraine: Carrier Aggregation Roaming .)

It said last month that it will deploy a Multiple Frequency Band Indicator (MFBI) in its 700 MHz LTE network by the end of September, which will support LTE roaming for any carrier with a compatible band 12 device. It is also working with handset makers to offer devices that support band 12 MFBI via a software upgrade. (See Apple's New iPhones Have 20 LTE Bands, VoLTE and VoLTE: So Close You Can Hear It.)

— Sarah Thomas, , Editorial Operations Director, Light Reading