The underlying technology
T-Mobile is the first U.S.-based carrier to deploy the 3GPP Release 10 of the Long Term Evolution specification, otherwise known as LTE-Advanced. The operator's new network can, however, more properly be considered LTE-Advanced ready. It is not offering features such as carrier aggregation -- the ability to bond radio channels to get more bandwidth and capacity -- since smartphones that can support that functionality are unlikely to be ready much before 2014.

• Why You Should Care About LTE-Advanced (Eventually)

The speeds
The speeds T-Mobile gets on its new network will very much depend on the amount of bandwidth it has to play with, which will vary with each market. Users peeping at T-Mobile's LTE signals in NYC and Baltimore have spotted two 5MHz LTE channels on the AWS band, which suggests a network that can achieve peaks of around 25Mbit/s to 30Mbit/s and less on average. Those numbers should get higher wherever T-Mobile has two 10MHz channels to use.

• How Fast Will T-Mobile's LTE Be?

The first markets
T-Mobile has said that it will have Las Vegas and Kansas City ready at launch. Users have also spotted signals in New York City; the D.C and Baltimore area; Houston; and other parts of Texas. T-Mobile hopes to cover 200 million people with the technology by the end of the year. T-Mobile's current networks cover 283 million people or 92 percent of the population of the mainland United States.

• T-Mobile's 4G LTE: More Details Emerge

Devices
T-Mobile has the Samsung Corp. Galaxy Note II. The BlackBerry Z10 smartphone will follow later this month.

• T-Mobile Starts 4G LTE Launch With Galaxy Note II

The future
T-Mobile is able to start this first stage of its nascent LTE-Advanced network deployment thanks to the spectrum and roaming rights it got from AT&T Inc. after that merger failed. Now it needs its proposed merger with MetroPCS to close in order to make the network a standout. If and when the MetroPCS spectrum gets layered in, T-Mobile will be able to add capacity and depth to its new network in the Northeast while still having some of the best 3G fall-back speeds available via HSPA 21 and 42.

• FCC Blesses T-Mobile/MetroPCS Merger

— Dan Jones, Site Editor, Light Reading Mobile