The U.S. Postal Service has signed up as a customer of AT&T in initiative to connect 5400 postal workers with BlackBerry push e-mail handsets.

The contract puts Research in Motion’s BlackBerry 8800 smartphones in the hands of managers and key staff, and later this year USPS will add the BlackBerry 8820, a Wi-Fi handset that will allow postal workers to transition between AT&T’s wide area GSM/EDGE network to post office Wi-Fi networks.

The deal encompasses more than just voice and e-mail communications, though. USPS Chief Technology Officer Bob Otto said the postal service will explore incorporating BlackBerry vertical applications into the mix, including location-based tracking, asset and supply acquisition and IT support and video training.

AT&T has been working with the USPS since 2001 when then Cingular began selling data services to the government agency.