Nexus One owners have been rockin’ Android OS v2.2 “Froyo” for weeks.  But millions of other Android-powered smartphones have been left high and dry, still running Android 2.1, 2.0 or – condolences – 1.x.

Android 2.2 won’t be limited to the Nexus One forever, though.  HTC, Motorola, Samsung, and the four major U.S. wireless carriers are each working to bring the latest version of Android to a number of existing handsets between August 1st and the end of 2010.

Here’s what we know – or think we know – about Froyo updates for existing handsets.

According to an AndroidSPIN tipster, Motorola will begin rolling out over the air (OTA) Froyo updates for the recently-released DROID X and the original Motorola DROID as early as next week.  The Verizon Wireless inside source believes August 6th may be the launch date for the 2.2 upgrade for these Motorola devices.

Similarly, the DROID Incredible, built by HTC, may also receive Froyo in the next week or so.  The (purportedly) final build of 2.2 for the Incredible has been leaked and is already available for download on XDA Forums, so an early August release doesn’t seem outside the realm of possibility. The AndroidSPIN tipster also claimed that the Incredible would be updated alongside Motorola’s DROID smartphones.

HTC plans to update other models in its Android lineup, too.  On Tuesday, August 3rd, the Sprint EVO 4G will be getting Froyo.  Later in Q3, the Desire, Wildfire and Legend will follow suit (some say the Desire will get its Froyo update as soon as this weekend).  The T-Mobile MyTouch family of smartphones (also built by HTC) are rumored to be getting Froyo, too, but this has not been confirmed.

Samsung’s Galaxy S smartphones – the AT&T Captivate, T-Mobile Vibrant, etc. – will be getting the 2.2 treatment, though the release schedule is pretty wide open.  While Samsung has committed to upgrade Galaxy S handsets in the UK come September, there have been no hints as to when U.S. versions will be updated.  Samsung isn’t talking other than to say that U.S. versions will get Froyo.

The Motorold DROID 2, which is scheduled to be released next month, will reportedly ship with Android 2.2 pre-installed.

Older and/or discontinued Android handsets including the HTC Eris and Hero, Motorola Devour and Backflip, Samsung Moment, and T-Mobile G1 are almost certain to never taste sweet, delicious Froyo – at least not officially.