AT&T is gearing up to roll out Mango today and presumably over the next few weeks. In doing so, they've updated their support page for customers to grab some information on the whole process.  The update advisory states:

AT&T and Microsoft have released software updates for the LG Quantum, HTC Surround, and Samsung Focus with Windows Phone 7. This update will install Windows Phone 7.5 (AKA "Mango"), and includes the following changes:

  • LinkedIn and Twitter integration
  • Contact groups
  • Facebook chat, check-ins, and photo tagging
  • New Bing search features including music and vision search
  • Improved web browser
  • Local Scout
  • Many more updates and improvements

While still not the update itself, it's more than obvious that AT&T wants to be out the gate here with Mango. Hopefully you'll be getting your notification soon.

Source: AT&T Support; Thanks, Tom A., for the tip!