Wirelessly posted (8700g: BlackBerry8800/4.2.1 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)
To unlock your BlackBerry for use on a carrier other than the one to which it is branded, you will need to purchase the unlock code from a vendor. A couple reputable ones advertise on this site--such as gsmphonesource.com.
If you have a good record with your carrier and good credit, they might do it for you for free, ask.
A new OS will not unlock it.
Answers to how to update the OS and get ringtones are at http://www.blackberryfaq.com/index.php/Main_Page