It's the last of the big four U.S. carriers to get a high-speed data network, but T-Mobile is finally gaining some much-needed 3G traction, with a second market—Las Vegas—now online, and an HSDPA-enabled phone on the way.

T-Mobile subscribers have been waiting a long time for 3G data access, which allows for speedy Web browsing, full-track music downloads, and streaming video. Until recently, most of T-Mobile's handsets—even hot numbers like the Moto ROKR E8, the various Sidekick phones, and the BlackBerry Curve—have been EDGE-only, or relied on Wi-Fi for fast data access.

That's all starting to change, though, with New York subscribers getting 3G access back in May, and now Vegas is getting the HSDPA treatment. (Click here if you need help with all the acronyms.)

T-Mobile says it hopes to have 20 3G markets ready by the end of the year, along with a new HSDPA phone (unnamed, for now) to take full advantage of the speedier network.

That said, T-Mobile still has a lot of catching up to do. The other three major U.S. carriers have all had big head starts—Verizon Wireless first launched its 3G network way back in 2003, for example—and they all have more than 200 3G markets each under their belts.

T-Mobile also has yet to launch any cool 3G services, such as video streaming or music download store. Indeed, T-Mobile's existing UMTS/3G handsets (you can check them out here) are pretty basic, and primarily use 3G for voice calls only.

Then again, T-Mobile will reportedly be first in line for an Android-powered phone—that's the new mobile OS pioneered by search behemoth Google, and it's expected to go on sale before the year is out.

And what about (finally) a 3G Sidekick? You know that'll make a splash.

Anyway—welcome to the 3G party, T-Mobile. Better late than never.

Related:
T-Mobile Launches 3G Network in Las Vegas [Phone Scoop]