It's always on, except when it isn't. Case in point: installed the TP on my Lumia 521 last night, and now data over T-Mobile does not work, stating I have a problem with my access point. WiFi works fine (which is how I'm typing this). A hard reset didn't resolve the issue.
try reselecting another access point if you have two ap or add another access point and put anything on it. make it active. then select the original access point.
try reselecting another access point if you have two ap or add another access point and put anything on it. make it active. then select the original access point.
Can't add a second one. When I try, it brings up the screen to enter all the settings. However, when I go to enter the settings, grabbing the ones from T-Mobile on my 925, it sits on a black screen with the Done icon greyed out and only the Cancel icon active. I have the keyboard active for a second and can type until I hit the Enter or back buttons, but don't see the text field anymore once I select it.