It looks like T-Mobile is getting their product testing company Centercode ready to start tests on their upcoming T-Mobile-At-Home (TAH) service. From what we hear, TAH is a wireless router-type device that broadcasts GSM and does VoIP through your broadband connection.
What this means exactly, we're not sure. But the GSM broadcasting could mean you're getting a stronger signal at home—like from a GSM repeater—and the VoIP is VoIP through the T-Mobile system. Most likely a flat rate for $X a month, or using up your minutes. All conjecture at this point until we receive more details after they roll out the test on August 11th.
They're only signing up customers over email and having them reply via email. People who call up customer service or go to T-Mobile stores cannot sign up. Read the PDF for more details.