T-Mobile is preparing to make changes to their wireless network that will make it compatible with Apple’s iPhone, the company announced today. They have partnered with Nokia Siemens Networks and Ericsson to roll out a $4 billion network upgrade that will enhance the company’s 4G network by rolling out broader LTE coverage.

T-Mobile’s current 4G network is reliant on HSPA+ technology. While arguably fast enough to earn the “4G” moniker, it is not as fast as the LTE networks currently operated by Verizon and AT&T (and currently being built by Sprint). Lacking sufficient wireless spectrum to build a full-sized LTE network, though, T-Mobile insists that HSPA+ counts.

The network improvements will utilize the wireless spectrum licenses T-Mobile acquired from AT&T due to the breakup of the proposed merger. T-Mobile is planning to bring LTE coverage to 75% of their top 25 markets (i.e., 18-19 markets). Their HSPA+ network is currently available in 229 markets.

Quibbling about what counts as 4G aside, though, this move is a big one for T-Mobile, as the expanded HSPA+ network will improve the carrier’s compatibility with the iPhone. The iPhone 4S is compatible with HSPA+ networks, but not with T-Mobile’s current AWS spectrum network. That incompatibility is the main reason that T-Mobile is the only one of the four major U.S. carriers that does not carry the iPhone.

Rolling out a more widespread HSPA+ network accomplishes two things for T-Mobile. First, it makes the carrier more attractive to iPhone users with unlocked phones who bring them to T-Mobile to get activated on the company’e network. Second, and more importantly, it makes T-Mobile more attractive to Apple. As T-Mobile itself has admitted, the lack of the iPhone has hurt the carrier tremendously in recent years.

T-Mobile has been hoping for the iPhone for a long time, and has hinted several times that they might finally be getting it. Back in January T-Mobile’s chief technology officer, Neville Ray, said that the next iPhone would carry a chipset supports T-Mobile’s AWS network. If that is so, then improving their 4G capabilities is bound to make T-Mobile even more attractive to Apple, especially considering the fact that the next iPhone will almost certainly have 4G LTE capabilities. By adding some LTE coverage and improving HSPA+ coverage, T-Mobile ensures that customers can take at least partial advantage of their device’s capabilities on T-Mobile’s network.

T-Mobile’s network improvements begin today and are expected to take much of the rest of the year. T-Mobile is expected to announce their quarterly earnings later this week.

What do you think? Would you switch to T-Mobile if they had the iPhone? Let us know in the comments.