It would be fitting to say that T-Mobile was derailed from its path in 2011. The company’s big break came in the form of a bid from AT&T to acquire the nation’s number four (and magenta-clad) carrier, but then as quickly as it swept into existence, the deal fell through.

Now, however, T-Mobile has a plan (the “Reinvigorated Challenger Strategy”) to get back on track and “get the business back to growth,” according to the release. This includes a $4 billion network modernization investment to evolve the carrier’s 4G network and help prepare for T-Mo’s LTE service in 2013.

The company will also be investing in the B2B segment, advertising, and attracting new MVNO partners. T-Mobile will continue to remodel its stores and make inroads in new territories, as well as expand the sales force by 1,000 employees.

That $4 billion in network investments will go toward installing new equipment at 37,000 cell sites and reworking their spectrum assets to get ready for an LTE launch in 2013. Now that the AT&T deal has fallen through, T-Mobile will receive new spectrum from the fall-out that will be the key to its plan to refarm spectrum.

This $4 billion investment will be spread out over time, but around $1.4 billion of it will be used over the next two years to go toward network improvement. Once LTE is up and at ’em, T-Mobile expects to offer service in “the vast majority of the top 50 markets,” with “20MHz service in 75 percent of the top 25 markets.”