I would be curious to know too. I am not exactly sure what the process is to unlock the phone as I have never done it. I have the procedure & the instructions from over at the XDA developers website though.
I call at&t to get the unlock code. But you need a different sim card from a different carrier to finish the process. I will be traveling to a different country, just hoping the unlock process I did before still good.
Depending on where you are traveling to, you shouldn't have to unlock your phone. Your Tilt should just plain work. You can go to the AT&T website to find out more. They have a World Traveler Plan that can be added to your account for $4.00 a month. All that does is reduces the cost per minute on the phone calls you will make while out of the country.
To unlock the Tilt is very easy. I called AT&T support and told them that I often travel oversees and would like to unlock my phone to be able to use local SIM cards. I was given the unlock code no questions asked.
I used T-Mobile SIM card from my Blackberry, entered the code when was prompted and the phone picked up T-Mobile as a provider.
I was also curious if I have to unlock again after upgrade to 6.1.
I just tried T-Mobile SIM card again and am happy to report that the phone is still unlocked after the upgrade, you don't have to do it again.
Regards