Microsoft's Windows Phone 7 makes its debut today on devices from AT&T and T-Mobile USA -- officially launching the U.S. leg of the Redmond company's make-or-break mobile comeback tour.

When it comes to apps, anyone thinking about switching to Windows Phone from the iPhone or Android will be in for a big adjustment. Some of the most important brands are on board for the Windows Phone 7 launch, including Twitter, Netflix, eBay, and Facebook. But the offerings quickly devolved as I browsed the Windows Phone Marketplace this weekend in the Zune PC software and on an HTC HD7 test device on loan from T-Mobile.

You know you've got some work to do when "Farting Dino" appears anywhere on your list of top-sellers.

But putting the apps aside and delving into the phone's core functionality, it's not hard to find stuff to like. The standouts in my early experience have been the deep Facebook integration, the Microsoft OneNote file synchronization and -- surprise, surprise -- the hassle-free sync with Google's email, calendar and contacts.

By way of background, I had spent some time trying out Windows Phones leading up to the launch, but this weekend was the first time I was able to get enough quality time with one to log in with my own Windows Live ID and other online accounts.

That level of personalization made a big difference.

The best part of Microsoft building Facebook functionality into Windows Phone 7's "People" hub is the way it quickly surfaces and integrates phone numbers and email addresses from Facebook friends -- the type of info that can easily get buried in the information deluge on the social networking service. (I wonder how many people will rethink the personal information they put on their Facebook profiles, once again, after they see the Windows Phone implementation.)

And the mobile version of OneNote, built into the Microsoft Office app, offers an easy way to take notes (and record audio and embed photos) in documents that can be automatically synchronized with Microsoft's Windows Live SkyDrive service.

Of course, Microsoft's own Windows Live services are strongly tied to Windows Phone, which leverages a Windows Live ID for Xbox Live and Zune integration, among other things. But as a heavy Gmail user, I appreciated the ability to also add Google contacts, email and calendar to Windows Phone using a simple login. Android users might not be so impressed, but as a longtime iPhone user, I haven't always found that process so easy with the Google calendar, especially.

To be sure, there are plenty of annoying quirks about Windows Phone 7. I've been struggling with the vertically oriented keys on the soft keyboard, for example. The core design of Windows Phone 7 -- with each screen providing only a partial window onto a larger page -- also takes some getting used to. At times I found myself lost in the interface, not sure where I was, until I hit the back arrow.

But overall, Windows Phone feels like a good effort from Microsoft.

Many users of existing smartphones will probably want to wait until the Windows Phone Marketplace grows and improves before seriously contemplating a switch. But Windows Phone offers some surprises that make Microsoft's new mobile OS worth considering, at least, for anyone upgrading from a basic cell phone.