Clearwire signed up another wholesale customer today with the addition of Jolt Mobile, a provider of prepaid and international calling for GSM phones.

The contract will help bolster Clearwire's wholesale customer base as Sprint, its largest wholesale WiMAX customer, prepares to phase out use of its WiMAX network. Clearwire has added four new customers for its WiMAX network since last fall: Simplexity, FreedomPop, NetZero and now Jolt Mobile. 

“Clearwire’s 4G network is a great fit for Jolt, enabling them to add 4G mobile data plans to their prepaid service portfolio," said Don Stroberg, Clearwire's senior vice president of strategic partnerships and wholesale, in a statement. "We’re thrilled to continue building momentum as the premier wholesale provider of 4G capacity to carriers in the U.S.”

Stroberg touted Clearwire's WiMAX network as a good fit for a "broad range of providers  including national and regional operators, MVNOs, and non-traditional entrants." 

Clearwire said its contract with Jolt Mobile may be eventually expanded to include access to its TD-LTE overlay network, slated for launch next year. 

“By partnering with Clearwire we aim to give our customers a compelling 4G alternative to higher-priced carriers," Jolt Mobile President Avi Yroshalmaine said in the announcement. 

Jolt Mobile's prepaid service runs on unlocked tri-band/quad-band GSM 900/1800/1900 phones and is compatible with locked AT&T phones and unlocked GSM phones from other providers. 

Clearwire is still heavily dependent on Sprint WiMAX customers for its revenue. Sprint's WiMAX customers comprise virtually all of Clearwire's wholesale revenue and accounted for more than one-third of its income during the first three months of this year. Wholesale customers also vastly outnumber Clearwire's retail customers - it had 9.7 million wholesale customers and just 1.3 million of its own retail customers during the first quarter.

Sprint said last year it would not develop any new 3G/WiMAX handsets this year, though it did announce a tri-mode hotspot in May compatible with 3G, WiMAX and its LTE network. It will support WiMAX customers through 2015, even after it stops selling devices compatible with Clearwire's network. 

Clearwire has said it is aggressively pursuing new wholesale customers. It announced yesterday it had joined the Rural Cellular Association, a move that will give it added lobbying clout and access to regional providers who could be potential customers.

Clearwire’s forthcoming TD-LTE network is a key part of its forward-looking strategy. The service is designed to provide supplemental capacity to companies looking to bolster their LTE networks in high-traffic areas like large cities. 

So far, Sprint and Leap Wireless International prepaid brand Cricket Communications have signed up for the network.  

"We believe that, as the demand for mobile broadband services continues its rapid growth, Sprint and other service providers will find it difficult, if not impossible, to satisfy their customers' demands with their existing spectrum holdings," Clearwire said in its most recent quarterly report. "By deploying LTE, we believe that we will be able to take advantage of our leading spectrum position to offer offload data capacity to Sprint and other existing and future mobile broadband service providers for resale to their customers on a cost effective basis." 

Clearwire expects to have its first 5,000 TD-LTE cell sites up and running by mid-2013, part of the 8,000 sites it currently has planned for the service. New York City, San Francisco, Los Angeles and Chicago are among the 31 cities scheduled to go live next year.