Bought used sim card for Blackberry rim 7520

the phone number should be retrieved from the sim card or carrier login procedure.

I had a few blackberry's, including a 75xx series one, and when I popped in another card (I have a couple of prepaid subscriptions for testing), the number always came up automatically.

Should work... If not, try contacting RIM/Blackberry support, but I doubt they'll still give support for the 7xxx series models... sorry

On the Main screen, scroll and select Options (looks like a wrench). Press Trackball.
Highlight Security Options.
Press Trackball.
Highlight General Settings.
Press Trackball.
Select the Menu key.
Highlight Master Radio Reset.
Press Trackball.
Select Yes.
Enter password 0000 or 000000 (both will work).
Screen will display: Master Reset Operation Completed Successfully.
Press escape button 3 times to return to the Main screen. From Main screen, scroll to Manage Connections. You may need to select the Menu key to see all of the options on the Main screen.
Press Trackball.
Scroll to Mobile Network.
Click Trackball so that a checkmark appears in the Mobile Network.
Press escape once and NXTL will display in upper right corner

hey, here is the way that you can fix this problem. You can go to your nextel delear nearest to you or even call your nextel company and have them switch it over to your newest phone!