Not getting unlock code prompt on AT&T Galaxy S4 after inserting new carrier's SIM card

[AC Question]

Here's the background:

Inherited friend's old AT&T Samsung Galaxy S4. Bought a prepaid account sim card from the current carrier I use for my ol' flip phone.

Submitted my phone's information to AT&T who in turn emailed me an official unlock code. Inserted my new SIM card (not yet activated as I'm still using the flip phone until I'm sure this is ok) and turned the phone on. As per AT&T's instructions, I was expecting to see the "Enter device unlock code" prompt that AT&T mentioned in their email. The device powered up, I went to the home screen and the only notice I saw was the "SIM no provisioned" notice.

So my question is this:

Is my phone actually already unlocked by it's previous owner OR will I not see the "Enter device unlock code" until I actually activate the sim card with the new carrier and the phone detects that it's not AT&T?

Thanks.

 

[anon(632115)]

The sim card hasn't been activated. If you were given a sim unlock code for the phone, it is locked. So, activate the sim, insert in phone, enter code, job done!

 

[Rukbat]

Try dialing #7465625*638*# on the phone (and waiting a few seconds). That should bring up the unlock code prompt.

 

[afulwell]

After entering the code #7465625*638*# and waiting for awhile, nothing happened. Any suggestions?