mariuss said:Wow that is odd why would u do that got upset on all ur friends ?
Most likely giving the phone to someone else
Are your contacts tied to icloud? If so turn off icloud sync and it will ask if you want to keep or delete your contacts. Select delete.
I have a 4S now and I'm giving the Iphone 4 to my assistant - I'll give that a go thanks!
If you are giving the phone to someone else, I would directly do a full reset to factory settings via iTunes (or on the iPhone via Settings > General > Reset > Erase All Content and Settings).
To just delete multiple contacts, the video below could be helpful: