T-Mobile issues and confusion

Over the past week or two ,I have begun to notice at my home and at customer sites, T-mobile wireless networks popping up as full strength networks(excellent signal strength) over shadowing the local inhouse WAP's, causing confusion and possible issues when my customers try to connect to the local WAP.

They cannot connect to the T-Mobile hot spots even though some of them have T-Mobile accounts.

Any ideas why this is happening?

Is this a job for the FCC?

Anybody else seeing this?

The area is San Francisco bay /San Jose Silicon Valley.