US Cellular has been teasing LTE roaming for ages, but they’ve been extremely quiet on who. New evidence, and sources, point to T-Mobile.

In late July, US Cellular announced that LTE roaming would initiate within “60 to 90 days” – but still wouldn’t say which carrier, at the time. US Cellular is the fifth largest carrier today, focusing on rural footprints, but has maintained a strong national coverage network via roaming agreements with Sprint and Verizon for CDMA 3G coverage.

And Sprint and Verizon jointly have benefitted from having free roaming on US Cellular – often times, if you’re wondering why your phone drops to 1x or EV-DO coverage out in rural areas, it’s because you’re actually roaming on US Cellular. So how does T-Mobile fit into all this?

T-Mobile is a GSM/UMTS carrier, so US Cellular roaming on 3G is not going to happen. There is however one thing that T-Mobile and US Cellular devices do agree on, and that’s LTE Band 12.

LTE Band 12 is what has powered T-Mobile’s resurgence in rural coverage areas. If somehow happen to have T-Mobile today, and you live in a rural market, it’s pretty essential that you get a phone that supports LTE Band 12. There aren’t many today, but that will change… to the point, we suspect, that T-Mobile will begin offering customers in rural zip codes free (or discounted) phone upgrades to Band 12 devices.

T-Mobile was rumored to be working with US Cellular, but implementation was a real concern. The two carriers are vastly different in configuration.

Moto E Was the Dead Giveaway

Awhile back, we (more than just) noted that T-Mobile was blamed by Motorola for a firmware update that revoked LTE Band 12 from the Moto E. This really isn’t legal behavior in the opinions of many – removing features from a device retroactively, after purchase, can get a company in hot water.

At the time T-Mobile (through Motorola, oddly) claimed that only T-Mobile devices can use Band 12 if they support VoLTE. We noted at the time this didn’t make a lot of sense – as there are various other scenarios that can cause LTE-only coverage, and VoLTE devices aren’t required there.

So we wondered what was so important about Band 12, that T-Mobile would require VoLTE to use it? Sources at T-Mobile have confirmed that it will be a roaming pact with US Cellular.

It also explains the LTE Band 12 redaction on Moto E. Without VoLTE on the second-gen Moto E, the phone would be constantly roaming for free on a (typically, stronger) US Cellular signal in rural markets, unable to make voice calls.

VoLTE Bridges the Platform Gap

By using LTE Band 12 for roaming, with compatible VoLTE stacks on both sides, T-Mobile and US Cellular can offer cross-carrier roaming, despite the CDMA-GSM platform divide.

This is an even bigger win for US Cellular customers. Customers with a VoLTE Band 12 phone on US Cellular, can now enjoy the coverage of nearly every network in America… save for AT&T.

A US Cellular VoLTE phone, if this deal is implemented, will be able to access US Cellular domestic coverage, free roaming on Sprint and Verizon CDMA networks, as well as voice and data on T-Mobile Band 4 and Band 12.

This is a major coup for both T-Mobile and US Cellular. It ensures T-Mobile phones will work vastly better in rural markets, and it ensures US Cellular phones will enjoy 4G LTE speeds in metropolitan markets.

This doesn’t leave Sprint and Verizon out in the cold, however. Sprint has begun adding LTE Band 12 to its devices, and Verizon has begun to see Band 12 phones trickle in as well.

The major difference there may be cost – it appears the T-Mobile/US Cellular alignment is a relatively fair trade, possibly to the point that money may not be changing hands. But, US Cellular, Sprint, and Verizon may be in a less cozy position than they once were – as a result. This could result in higher roaming rates for Sprint and Verizon to offer rural LTE coverage, for customers traveling on those networks.

However until a cross-carrier VoLTE solution is implemented in device firmware, it’s questionable if today’s Sprint and Verizon phones (aside from a select few like Google’s Nexus 6 and iPhone 6) will be able to utilize US Cellular VoLTE. For most Android devices (aside from T-Mobile and US Cellular VoLTE devices), cross-carrier roaming VoLTE will begin in the Android Marshmallow era.