Both operators are deploying their nascent LTE services in different blocks of the 700MHz spectrum they got through auction and acquisition. AT&T has spectrum in lower B- and C-bands, known as class 17, while Verizon has class 13 spectrum in the upper C-Band.
This means that even if there were agreements in place to allow users to roam onto either operator's LTE network when out of the range of their home network coverage, the device would need two 700MHz radio frequency chips on board to allow it to happen. LR Mobile doesn't know of any such devices yet. The FCC, however, is now considering making the whole of 700MHz interoperable. It has put out a call for comment and is exploring potential interference issues.
The U.S. currently isn't alone in its LTE roaming inabilities:
"There's no roaming between LTE networks yet," notes Doug Suriano, CTO of network vendor Tekelec He explains that the standards have been written for it and that Tekelec's latest signaling system supports it.
Devices can roam between LTE and 3G networks, he says, but roaming between different LTE networks is expected to be implemented by operators sometime in the next 12 to 18 months.
Why this matters
A more unified 700MHz band should make 4G services and device choices easier for users and smaller carriers that need to support the frequencies in their own hardware. AT&T and Verizon haven't, however, been in any rush to ink roaming agreements yet.
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— Dan Jones, Site Editor, Light Reading Mobile