Wondering if you should be considering that T-Mobile 4G phone purchase now that the merger plan has come to light? Read on.

With the news of the AT&T / T-Mobile merger spreading like wildfire, there have been rumblings about the network compatibility implications of the deal. More accurately, how the merger will affect consumers' use of 4G handsets on their respective carriers.

Make no mistake - it has been confirmed that AT&T will slowly disassemble T-Mobile's 4G HSPA+ network over time, converting those HSPA+ bands (the "AWS" spectrum) into LTE frequencies. Consumers without at least a Wikipedia-level of 4G knowledge will likely ask why this is necessary if both carriers already use HSPA+ "4G."

They may know that it's generally not possible to use a T-Mobile phone to get 3G while on AT&T, and vice versa. This is because the carriers use two different frequency bands on their respective 3G networks:

  • T-Mobile 3G: 1700/2100MHz ("AWS" spectrum)
  • AT&T 3G: 850/1900MHz

When upgrading their networks to HSPA+, both carriers retained these spectrums for the deployment of their "4G." This is because HSPA+ uses the same hardware and networking infrastructure (the UMTS system) as standard HSPA, and only requires software changes  and more antennas on existing arrays, while it still transmits a signal which standard HSPA  3G phones can utilize. So, essentially, it's the same network - just beefed up.

Both AT&T and T-Mobile's "4G" HSPA+ networks retained the frequencies of the existing 3G networks, and so retain their incompatibility.

This means that your Inspire 4G, myTouch 4G, Galaxy S 4G, G2, and Optimus 3D will never experience a unified HSPA+ experience. None have the proper radio equipment to interface with their former competitors' HSPA+ networks (or 3G at all, for that matter). But there is an exception to the rule: the yet-to-be-released LG G2X. This device will be backwards compatible with AT&T's "4G" HSPA+ network.

You can also probably expect such compatibility on upcoming T-Mobile "4G" phones  this year (at least we hope so), though whether AT&T will do the same is unknown, since there isn't much of a need if they'll just be taking T-Mo's 4G offline anyways.

How long it will take AT&T to fully dismantle T-Mobile's 3G/4G network remains a big question, and that depends largely on how quickly AT&T plans to deploy its LTE network starting later this year. When it does happen, T-Mobile's current 3G and 4G handsets will start to lose data coverage.

Take this information into consideration when deciding your next T-Mobile Android purchase, it may come into play in a not so great way down the road.