The Samsung Galaxy S2 (SII) is the successor to the Samsung Galaxy S. Here's how to unlock the Galaxy S2 so you can insert your own SIM card.
Step 1. Check the network status
Check if the phone has a network lock by typing *# 7465625# on the keyboard. Sometimes a phone has no lock while you still see the network logo.
Step 2. Find the IMEI number of the phone
Type *# 06# on the keyboard. Now the IMEI number will appear in the screen. Make a note of this number for later reference.
Step 3. Contact your carrier and request an unlock code
Sometimes the provider only gives you a code after a certain number of months. If you don't get it you can buy a code from an unlocking website.
Step 4. Get the unlock code
You can get it over the phone, from your carrier, or in an email you receive from an unlocking website.
Step 5. Insert a new SIM card into the phone
Remove the old SIM card and insert the new SIM.
Step 6. Turn on the Galaxy S2
You will now be asked for the unlock code.
Step 7. Enter the unlock code
Type the code you obtained on your keyboard and your phone should now be unlocked!