which sim card with unlock code?

I have a Nokia 3595 that used to be used with T-mobile. I want to use it with an Att Wireless sim card as I was with them before they switched to Cingular.

Do I enter the unlock code with the old T-mobile sim card inserted or with the new Att sim card inserted?

Thanks

you put the code in without any sim in... ;)
be carefull with the codes, you only get 5 try's
before its hard locked.

use code 7 first.. ;)

On some new models, you have to enter the code with a NOT ACCEPTED card, no other way.
and even with old models with a not accepted card it works too, always.
BR