T-Mobile has requested the iOS users to not update to the iOS 10 yet, in case their handset is an iPhone 6 Plus, iPhone 6 or an iPhone SE. The information comes directly from the CEO of T-Mobile, John Legere.
The reason behind such a message is the fact that some iPhones actually lose connection with the T-Mobile network after the update. The existing bug in the iOS 10 temporarily disconnects your iPhone from the T-Mobile network forcing you to restart your handset to regain the connection. This may seem like a simple solution, but it is not worth risking such an uncertainty especially when you are waiting for that important call from your frustrated boss.
The root cause of the bug may very well stem from instability in the frequency spectrum at which the iPhone operates after the update, some bands may not have been fully configured leaving you with a lost connection when the phone automatically switches between bands.
Apple has already acknowledged the issue and is working on it. An estimated time for the fix has been stated to be 48 hours. In case you have already updated your iPhone to the iOS 10, then your only resort is to restart the phone whenever the connection is lost, until the fix arrives.