How do you unlock a T-mobile phone to work with At&t simcards? How does this work?

hi there are many ways to unlock the mobile from the network .it will be helpful for me to guide you the exact place if you had specified the model of your mobile .if your mobile model is nokia then get codes at unlocking4free here they ask the imei number of your mobile finally they generate codes to unlock your mobile at free of cost.here in the above site they provide unlock codes for older mobile models.

What is your mobile brand name&model? If you want unlock your mobile phone you can visit this site Mobile-unlocker.com here you can get the code and unlock your mobile easily. To get the code you have to mentioned your mobile brand name,model,which country is locked now,network provider and imei number. Then they send unlock code through email.