Using a ATT Branded 640 XL on Tmobile

[Sedp23]

I have a friend on a 640 XL she unlocked from att, she put her tmobile sim in and it works fine but when she's on a call she can't use her data

Is there some kind setting she needs to change in sim settings so she can use data while on calls?

 

[libra89]

Check the APN and make a new one to match the ones that T-Mobile uses.