AT&T has completed its carrier testing of Windows Phone 7 and is preparing to push the update out to some devices on April 19, WinRumors has learned.

AT&T issued an internal email to its support personnel this week detailing Microsoft’s NoDo Windows Phone update. It appears that LG Quantum and Samsung Focus devices will both receive the NoDo update on April 19 whilst updates for the HTC Surround are scheduled for a mid-May release:

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. Approved updates for the HTC Surround are scheduled for availability in mid-May and will be communicated once approved.

Microsoft is planning to release two new Maintenance Release (7008 & 7390) updates that require a three-phase installation. The update installation process includes:

• Installing Zune software
• Installing the 1st (7008) MR which prepares the WP7 device to accept the enhanced (7309 “NoDo”) update
• Installing the 2nd (7390 “NoDo”) MR update that adds new device functionality

Customers will receive a notification starting on 4/19 advising them of an available update for their phone. Once the customer completes the 7008 update, they will be able to immediately update their devices to 7390 (NoDo) by disconnecting and re-tethering their phone to their PC. If the customer does not immediately update their device to 7390 (NoDo), they will receive a notification that an update is available within three days.

The Headliner for the 7390 (NoDo) MR is that it adds Copy/Paste functionality but additional functionality is included that is unique to AT&T.

SUPPORT PROCEDURES
My CSP will be updated for launch. If customers should have additional questions or issues with this update, please refer the customer to LG or Samsung for additional support following standard policies and procedures.

Important Notes
Installation of the 1st (7008) maintenance release is required before the 2nd (7390 “NoDo”) maintenance release can be successfully loaded on the Windows Phone 7 devices.

Microsoft is still officially promising “early April” for AT&T to finish their carrier testing. Despite the delays some Windows Phone 7 owners (WinRumors included) have been able to force the NoDo update onto their devices. The method involves a registry key change and some tinkering to make the phone appear as if it’s located in Europe. The method has been confirmed to work on a variety of devices, including AT&T’s popular Samsung Focus device. If you’re interested in seeing how NoDo runs on the Samsung Focus then check out our video overview here.

Microsoft recently warned against the use of workaround methods to receive NoDo. The words of warning followed a recently distributed ChevronWP7 Updater. ChevronWP7 developer Chris Walsh released an update application that bypassed the carrier check for Microsoft’s latest Windows Phone update, codenamed “NoDo”. Walsh began distributing the updater last week but has since removed the download, at the request of Microsoft. The software giant warned that “You might not be getting the important device-specific software we would typically deliver in the official update. Or your phone might get misconfigured and not receive future updates.”

Thanks to anonymous for the news tip