AT&T has completed Windows Phone 7 "carrier testing" and plans to push the Windows Phone "NoDo" update out to some devices on April 19, revealed AT&T's internal email.
In this matter, AT&T sent an email to its support personnel detailing Microsoft's NoDo Windows Phone update. The email reads: "Effective April 19, 2011, new Microsoft maintenance release updates will be available to AT&T customers with existing LG Quantum and Samsung Focus Windows Phone 7 devices." Although, "approved updates" will be available in "mid-May" for the HTC Surround.
Here's the complete email: