Before you sell or after your purchase, we need to wipe the traces on the machine. 
There are two ways to delete contacts on BB:
1 – Back up, delete contacts, messages on BlackBerry Desktop … computer.
Connect BB to computer> open BB Desktop Manager> Backup & Restore Select> Advanced> then want to delete and press select Clear
2 – Remove directories directly on your BlackBerry:
Settings> Options> SERCURITY Options> click wheel select Wipe handheld
Machine will require text entry on the blackberry and then the machine will reboot.
