Low-cost wireless carrier MetroPCS Inc. (NYSE: PCS) is proposing a $7.5 billion merger with rival Leap Wireless International Inc. (Nasdaq: LEAP).

MetroPCS announced today that it wishes to acquire Leap Wireless for $5.5 billion in stock plus $2 billion in acquired debt. The offer caps years of speculation about a merger between the cut-rate carriers. Leap, however, has not yet responded to the MetroPCS offer.

MetroPCS undertook a $1.15 billion float on the NYSE this Spring. The operator has said before that the money could be used to expand its subscriber base through acquisition. (See MetroPCS Eyes $1B IPO.)

MetroPCS claims around 3 million subscribers in California, Florida, Georgia, Michigan, and Texas. Leap operates in over 22 states and has a customer base of over 2 million users. A merger between the two companies would create one of the largest local low-cost operators in the U.S.

Larger nationwide operators such as AT&T Inc. (NYSE: T) and Verizon Wireless have been picking off local operators recently in a bid to bolster their user base and improve nationwide coverage.

AT&T bought Dobson in June this year. Verizon picked up Rural Cellular in July. Number one local player Alltel Corp. (NYSE: AT), meanwhile, is trying on a private equity deal for size. (See Verizon Ropes Rural Cellular , AT&T to Buy Dobson for $5.1B, and Alltel Accepts $27.5B Buyout Offer.)

MetroPCS was up $1.11 (4.07%) to $28.40 in late afternoon trading on the news. Leap, however, jumped $10.82 (14.92%) to $83.32.

— Dan Jones, Site Editor, Unstrung