US GSM operator T-Mobile USA is expanding its 3G network ahead of the launch of the much hyped Google phone, the G1.

Based on the Open Handset Alliance’s (OHA) Android operating system, the G1 will go on sale at T-Mobile stores on Wednesday, costing $179 with a two year voice and data agreement.

This week, T-Mobile has added 3G coverage in the Sacramento, California, area as well as Memphis, Tennessee, and Tampa, Florida.

T-Mo said it will launch 3G service in and around the Washington, D.C., area in late November, taking the number of locations with 3G coverage to more than 120 major cities across the top population centres nationwide. The operator said its 3G network can deliver download speeds of up to 1Mbps.

The G1 is built by HTC and boasts a touchscreen and trackball as well as a slide out QWERTY keyboard. 3G HSPA, EDGE and wifi provide the connectivity along with GPS, while the camera weighs in at 3 megapixels. The software features Google apps including Google Maps with Street View, Gmail, Google Talk and YouTube, as well as a full HTML web browser and Amazon’s MP3 store. Applications are discovered and added via the Android Marketplace.