Unlocking the Blackjack

[Guest su6oxone]

So I called AT&T to get an unlock code for my Blackjack and gave them the IMEI code, and they said they would send it to me in 5-7 days. With this unlock code, will I be able to then use the Blackjack with any GSM carrier just by inserting the SIM card? I've never unlocked a phone so I'm not quite clear on what unlocking specifically does. Thanks in advance.