Sprint Nextel (NYSE: S) had better step on the accelerator, stat! The mobile network provider's biggest competitive advantage is going up in smoke soon.

The 800-pound telecom gorilla Verizon (NYSE: VZ) plans to open 4G data networking service in 38 metro areas and 60 airports by the end of 2010. That initial rollout would cover as many as 100 million Americans while Sprint's 4G partnership with ClearWire (Nasdaq: CLWR) is advertised as covering a mere 40 million consumers today, though the company has previously stated its goal is to cover 120 million consumers by the end of 2010. Moreover, Sprint tells you to expect average download speeds in the 3-6 megabits per second range but Verizon aims for 5-12 mbps "in real-world, loaded network environments." Sprint's early-bird advantage is going up in smoke.

AT&T (NYSE: T) is not far behind Verizon in its 4G plans, while Deutsche Telekom subsidiary T-Mobile is touting its intermediary HSPA+ solution instead, offering near-4G speeds albeit on a less efficient 3G-class infrastructure that will cost more to operate in the long term and cannot be upgraded nearly as far as the LTE and WiMAX 4G solutions.

If Sprint wants to make hay while there's hay to be made, the time to nitro-boost its marketing programs would be right now. Sprint already has two 4G-capable smartphones on store shelves today in the Samsung Epic 4G and HTC EVO 4G. Verizon will need to hit up its favorite partners, HTC, Motorola (NYSE: MOT), and Samsung, for 4G hardware even if the networks are ready for liftoff.

Make a land grab now or forever hold your peace, Sprint. Once the bigger boys invade your 4G turf, you'll have to sell your services on pricing and the lack of irksome data plan caps instead, which seems to be a much less profitable way to go than the soon-to-be-obsolete "fastest network" message.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. Sprint Nextel is a Motley Fool Inside Value recommendation. Try any of our Foolish newsletter services free for 30 days. True to its name, The Motley Fool is made up of a motley assortment of writers and analysts, each with a unique perspective; sometimes we agree, sometimes we disagree, but we all believe in the power of learning from each other through our Foolish community. You can check out Anders' holdings and a concise bio if you like, and The Motley Fool is investors writing for investors.