The first three US phones running Microsoft's Windows Phone 7 OS go on sale today, with the Samsung Focus (4 stars) and HTC Surround (3 stars) debuting on AT&T and the HTC HD7 (3.5 stars) becoming available on T-Mobile. All three phones cost $199 with a two-year contract.

We have full reviews of all three of the launch devices (just click on the product name above), and we like the Samsung Focus best. The Focus has a bright Super-AMOLED screen and is just the right size for navigating Windows Phone's colorful interface, playing XBOX Live games and watching Zune videos. The HTC Surround has a large slide-out speaker, but we found it just wasn't as good all around as the Focus. The HTC HD7 has a huge 4.3-inch screen, but we docked it points for not supporting T-Mobile's new, heavily promoted "4G" HSPA+ network.

The best may be yet to come, as three more Windows Phone 7 devices are already waiting in the wings. The Dell Venue Pro, for T-Mobile, is getting positive advance buzz for its vertical QWERTY slider form factor. That gives the Venue Pro the advantage of a full keyboard without suffering from Windows Phone 7's trouble with horizontal screens. The LG Quantum, for AT&T, will have a more common horizontal QWERTY sliding form, as will next year's HTC 7 Pro, which will come out on Sprint.

As of yet, Verizon Wireless is the only major US carrier not to have committed to releasing any Windows Phone 7 devices. The company has previously said it will probably release at least one Windows Phone 7 device in 2011.

Windows Phone 7 is backed by a massive, if peculiar marketing campaign centered around the idea that people should use their smartphones less, and that Windows Phone 7 is a quicker and more direct way to get what you need done. That said, although Windows Phone 7 has Microsoft Exchange and Office support, Microsoft isn't targeting the new OS at business yet; it's for individual "life maximizers," according to Microsoft.

With devices in stores, the next battle will come over apps. Microsoft currently has about 1,000 apps in Windows Phone 7's marketplace, and has delivered an unusually easy-to-use set of tools for programming apps. The first games, especially, have already vaulted past the quality of the average Android-based game. But Microsoft has an uphill battle to draw application developers (and thus users) away from the popular iPhone platform and from Android and BlackBerry, which have far greater installed bases than Windows Phone 7 does so far.

Keep an eye on PCMAG.com for reviews of all the Windows Phone 7 devices as we get them.