Is there a free code i can use to unlock a htc hd2 phone that was tmobile now i want to use it with at&t

The best way usually is to contact T-mobile for an unlock code for your handset model. They seem to oblige if you have been in their network for more than 4-6 months. If they are unwilling, please consider using a paid and reliable service like http://www.unlock-zone.com/. I am afraid free codes will not be reliable and may lead to loss of data on your cellphone.

Hope this helps.

-regards,
Mrigs

If the phone is out of it's subsidy (you've paid t-mobile back for the phone) then they should provide the unlock code for you.