For data you need roaming data on, not just cell data.
If your phone is not set for automatic networks then change it to select a network automatically.
Then of course you need to be in a T-Mobile coverage area. That's not the responsibility of Public Mobile.
Once connected then data and text should work fine (if in coverage). Talk needs 2G coverage available. This is where the problem is. Also some phones can't drop down to 2G anymore. What make and model phone are you using?
