Well, this news kind of came out of nowhere.  After reporting that the G2, one of the newest Android phones on the market, would be getting an OTA update, we learn that the myTouch 3G, one of the oldest Android phones on the market, will also be receiving an update.  The myTouch 3G will be updated to Android 2.2 beginning tomorrow, with the staggered roll out expected to continue until October 25th.  Included in the update is all of the usual Froyo goodness, new home screen features, remote wipe, and a fully-integrated Exchange experience.  Unfortunately, it appears that this update is only for original myTouch 3Gs, which excludes those myTouches with a 3.5mm headphone jack, the Fender limited edition myTouch 3G, and the myTouch 3G Slide.  Check out the full list of improvements that the myTouch 3G will get down below.

This is huge news for those of you still clinging to your OG myTouch 3Gs, especially since we originally heard about T-Mobile's plan to bring Android 2.2 to the device back in June.  The update should make that aging myTouch 3G feel like a completely new handset, and may even fend off the desire to upgrade to the new T-Mobile myTouch (maybe).  Just remember that this will be a staggered OTA upgrade, so don't panic if you don't get it tomorrow.  When your myTouch 3G does finally move up to Froyo, you'll come back and tell us, though, right?

Primary Improvements Included with This Update

• New Fully Integrated Exchange Client

• Improved security: Numeric pin and alpha-numeric password options have been added to unlock the device. Exchange administrators can enforce password policy across devices.

• Remote wipe: In the event a device is lost or stolen, Exchange administrators can remotely reset the device to factory defaults to secure data.

• Exchange calendars: Exchange calendars are now supported in the Calendar application.

• Auto-discovery: With just a user name and password users can easily set up and/or sync an Exchange account (available for Exchange 2007 and higher).

• Global Address Lists look-up: This functionality is now available in the E-mail application, enabling users to auto-complete recipient names from an entire directory.

Faves

• Faves Gallery gives customers quick access to the 20 people who matter most.

• Customers can scroll through their Faves Gallery and instantly see the most recent communication from their top 20 Faves – calls, texts, emails, instant messaging, and social networking updates – and respond in a flash.
  

New Home Screen Features

• Home screen Tips widget provides tips on how to configure the home screen with shortcuts and widgets and how to make use of multiple home screens.

• Market widget lets you keep on top what’s hot on Android Market, showing featured apps right on the home screen.

• Live wallpapers are available on Android Market, such as Aquarium, Google Maps and many others.

• Phone, All Apps and Browser now have dedicated shortcuts on the home screen, making it easy to access them from any of the five home screen panels.
  

Improved Communication Features

Gmail app enhancements:

• Include quoted text from the body of an e-mail message Navigate quickly using on-screen previous/next buttons Identify e-mails using colored labels See inline images in messages

• Calendar app now supports multiple Google and Exchange accounts

• Google Talk app lets users search for buddies from the Search key

• Google Voice app now uses Inbox Synchronization so new messages are received in a matter of seconds

• Quickcontact is now available in Gmail, Google Talk, and Google Voice, right from your device. Users tap on a contact image to access various ways to reach that person, such as call, SMS, e-mail, etc.
  

Other: Improvements to the camera and camcorder, ability to add multiple languages to the keyboard, enhancements to Google Maps, YouTube app, Facebook app, and Twitter app.

UPDATE: TmoNews has posted a T-Mobile doc with all of the info.  Looks pretty legit, folks!

Via TmoNews