T-Mobile US (NYSE:TMUS) has leased its spectrum to other carriers in an effort to expand its LTE network. However, it's unclear how extensive those efforts have been or how T-Mobile's work with other carriers compares to similar programs from Verizon Wireless (NYSE: VZ) and Sprint (NYSE: S).

"We're always exploring opportunities to enhance America's fastest 4G LTE network," a T-Mobile spokesperson told FierceWireless. "Over the years, we've bought, sold and leased spectrum to roaming partners and we'll continue to discuss additional opportunities that will benefit our customers."

T-Mobile declined to comment on how many carriers it has leased spectrum to, what spectrum bands were leased, or how much territory those leases cover. "T-Mobile is always looking for the right opportunities to improve its network," the spokesperson said in a statement. "This includes spectrum swaps, leasing spectrum and roaming agreements. We'll continue to discuss additional opportunities as they arise and make the best decision to benefit our customers."

T-Mobile's spectrum-leasing efforts appear to be a less formal version of Verizon's LTE in Rural America (LRA) program, which was inaugurated five years ago. To date, Verizon has signed up 21 rural and smaller carriers to the program, and 19 have launched LTE networks via the program.

Under the LRA program, LRA members lease Verizon's 700 MHz Upper C Block spectrum. They then build out their own networks and sell service to their own customers, but have access to Verizon's network vendors, LTE device portfolio and their subscribers can roam onto Verizon's nationwide LTE network and the networks of other LRA partners. Verizon customers can also roam onto the networks of LRA members. The program allows Verizon to quickly and cheaply build out rural areas.

Verizon noted this week that there are 224,000 square miles covered under LRA agreements and 100,000 square miles with live LTE networks. Fully 2.9 million people are covered by the leases and there are more than 900 LTE cell sites live in LRA territory.

In an interview with FierceWireless, Philip Junker, Verizon's executive director of business development and the head of the carrier's LRA program, said that the LRA members collectively have "hundreds of thousands" of customers, though he declined to go into specific numbers. "We're pleased with the customer growth and I think they are, too," he said.

Verizon's LRA members are Bluegrass Cellular; Cross Telephone; Pioneer Cellular; Cellcom; Thumb Cellular; Strata Networks; S and R Communications; Carolina West; Custer Telephone Cooperative; Convergence Technologies; Ketchikan Public Utilities Telecommunications; Chariton Valley Communication Corporation; Appalachian Wireless; Northwest Missouri Cellular; Chat Mobility; Matanuska Telephone Association; Nemont's Sagebrush Cellular brand; Copper Valley Telecom; Mid-River Communications; Phoenix Wireless' Wireless Partner brand; and Triangle Communications.

The only two that have not launched service are Triangle Communications in Montana and Wireless Partners in Maine.

Sprint operates a similar leasing program. The carrier counts a total of 27 carriers in its rural LTE program, covering 565,000 square miles in 27 states and a population of more than 38 million people.

The carrier's in Sprint's program get access to Sprint's LTE network and device portfolio, and in some cases they lease Sprint's spectrum. Sprint is also working with its rural partners to get them access to network infrastructure for the 2.5 GHz band, a key element of Sprint's tri-band LTE Spark service.

A Sprint spokeswoman did not immediately have a comment on how many carriers in its program have actually launched service.

"We applaud Sprint's efforts," Junker said. "We have long been an advocate for bringing 4G broadband to rural communities."

For more:

- see this Verizon page

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Correction, May 15, 2015: This article incorrectly identified MTPCS' Cellular One brand as an LRA member. They are no longer a member of Verizon's LRA program.