Fixed Now...
Just got the following message from T-Mobile:
"Important Message: Current version of iOS 10 has connectivity issues. An update is now available. Please go to Settings->General->About to update your iPhone."
This triggers an update to ....
(wait for it....)
Carrier SETTINGS....
<SARCASM>so... I guess it was apples fault? </SARCASM>
how bloody disingenuous... making it look like it was an iOS bug rather then a T-MOBILE bug....