No password needed!
Tmobile has a very detailed coverage map at http://compass.t-mobile.com/
but ironically they do not give public access to this map. If you are a tmobile customer you have a right to easily access this information. Please call t mobile at 1-877-878-7326 and demand to have access this detailed map.
You can search the map by city, state, and address. The map shows coerage with different shades of color. At this time only dealers and tmobile its self have access to this map. Tmobile remember we are the customer and your coverage map is there for our benifit.. so open up access to atleast your customers.