ATT iPhone 4 unlock granted... how does it go from here?

Here is the situation.

I sold the iPhone 4 to a co-worker when I got my iPhone 5, before doing so I removed my sim and destroyed it.

He had previously told me he had a friend who was going to unlock and jailbreak it for him, that's why he wanted to buy it. To put it on T-Mobile for his kid.

On his part, it seems there was some miscommunication about what unlocking is and how to do it.
He hasn't been able to contact his friend...

So, I decided to help him out by requesting via the ATT website for an unlock.

The unlock was authorized and I received an email with instructions along with this link for help
http://support.apple.com/kb/HT5014

What needs to be done from here, by whom, with what sim card, and with whos iTunes account?

I no longer have a sim for the iPhone 4. He has the iPhone.

Can't seem to find an answer anywhere and we are about to start trial and error over the next few days...

Any help is appreciated!