Help needed! T-mobile galaxy note with At&t sim

[szl125]

My friend gave me this T-mobile version of galaxy note (I'm not sure if it is locked or unlocked) and I inserted my AT&T SIM card.

The phone recognized my SIM and voice calling & text messaging is working fine.

However, it does not have 3G/4G connection.

The only way I can use the data is through Wifi.

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Do I need to unlock this phone in order to use 3G or 4G data?
Or
Is this phone already unlocked (since my AT&T SIM is recognized and working) and I need to something else to use the 3G/4G?

 

[landovr]

You probably need to change the apn settings. Try going to settings/wireless and networks/mobile networks/ and click on access point names and see if there is an option for at&t