Signal is not required to unlock a Blackberry 9720. All you need is a non accepted SIM card. Once you enter a non accepted SIM card in your Blackberry 9720, it would prompt you to enter an unlock code. You can get the accurate unlock code for a Blackberry 9720 from SuperUnlockCodes.com
at affordable cost. Good luck.
1 - Switch ON your Blackberry 9720 with your current network/service provider's SIM card.
2 - Using the menu
go to Settings Menu
-> SIM card
and press select.
3 - While holding the SHIFT
key, type mepd
.(NOTE: You may not see any text appear on the screen while typing mepd)
4 - You should now see the five locking categories listed.
5 - While holding the SHIFT
KEY, type mep2
.(NOTE: You may not see any text appear on the screen while typing mep2).
6 - Release the shift key.
7 - You will now be prompted to enter the Network MEP code. (it will also state how many attempts left)
8 - Enter the Unlock Code.
9 - Enter Return/Enter.
10 - The Blackberry 9720 should then be unlocked.