After only selling phones in the U.S. through AT&T (NYSE: T) for years, Sony (NYSE: SNE) Ericsson (NSDQ: ERIC) announced today it’s expanding its distribution network to include T-Mobile USA. This is good news for both parties. Sony Ericsson has been affected by slower handset sales in part because of a weaker economy but also because its handset mix has lacked the variety of devices that other manufactuers have, such as full Qwerty keyboards and touchscreens. For T-Mobile USA, it will add another supplier for its new 3G network. The handset called the TM506 will run on T-Mobile’s 3G network on the 1700/2100 spectrum band. The clamshell will launch in early September, has a two megapixel camera and is being advertised as having an “exceptional” Web experience.