Home Internet discount bundle.

We have had no trouble with T-Mobile, customer for 10 years.  When TMI became available in this area we thought about it for a few months (i.e., did nothing), but decided to try the 10 day trial.  After one week we cancelled our cable company and are using TMI.  The download speeds (for us) were usually equal or better than our cable, upload speeds were a bit slower, but for what we are doing we really don't see a quality difference.  I say usually because we occasionally go some slow tested download speeds, but still didn't see a difference in quality of service.

The T-Mobile "price lock" is a real thing.  We only recently changed our plan because our son moved out and got his own line.  Previously we had the plan we signed onto at the beginning.  The price never varied and we liked it.  We got a better deal than we had before with the same service going with one of their geezer plans (yes, I can say that because I am one), otherwise there would have been no need to change.

Given all that I agree with copz1998, if you have no issues you may as well stay with ATT.  However if you have any issues with ATT, talk to the TM store sales/tech support people and see what you think.  You can probably run both systems as a trial if they both have trial periods.  Give it a shot and let us know what you find.