Why Sprint is pushing LTE for 100 cities in “coming months”

Sprint(s s) is continuing its big network push for fast LTE service, announcing on Monday that 100 cities will receive LTE in the “coming months.” That’s not a very precise timetable, but what is definite is that Sprint is quickly trying to catch up to its U.S. rivals who already offer LTE. Sprint’s key differentiator is unlimited mobile broadband service, which can help it keep or attract customers, provided it gets the LTE network up and running sooner rather than later.

In the press announcement of its network plans, Sprint says the following major markets are part of the LTE expansion over the coming months: Boston; Charlotte, N.C.; Chicago; Indianapolis; Los Angeles; Memphis, Tenn.; Miami; Nashville, Tenn.; New Orleans; New York; Philadelphia; and Washington, D.C. A full list of the 100 cities where Sprint is deploying LTE during this phase can be found here. The carrier expects to complete its 4G LTE network build by the end of 2013, essentially covering its current 3G footprint of today with LTE.

What’s the rush? Sprint’s bet on WiMAX back in 2008 cost it both money and time as rivals chose LTE for its speed and GSM compatibility. As a result, Sprint has watched Verizon(s vz)(s vod) roll out 371 LTE market since 2010 while AT&T(s t) is at 60 and growing. Even T-Mobile is on the LTE bandwagon: It has a strategy to refarm spectrum and launch its own LTE 4G service. Add all this up and Sprint’s early mover advantage in U.S. 4G is long gone and so too might customers be who can’t wait for the carrier’s network upgrades.

On a related bet, Sprint decided to spend billions to bring Apple’s iPhone(s aapl) to its device portfolio in 2011. It will take several years to get that money back and even longer if Apple does add LTE support to its next iPhone as the Wall Street Journal reported last Friday. Sure, Sprint may offer unlimited data plans, but if a shiny new iPhone is stuck on an older 3G connection that’s up to 10 times slower than LTE, will consumers pick a Sprint iPhone or one from a Sprint rival?

History suggests faster speeds are trumping unlimited data; at least when it comes to the iPhone.