This could be due to a few different things but more information is required to find out which one it is:
Does the SIM card you are using match the company that your friend was using
Is the phone blacklisted, which would happen if your friend recieved his new phone as an insurance claim or fault?
Are you connected to the correct network?
I used to work as a handset faults advisor and we had many problems like this with the 6500, I think it's best if you call your phone company and go through a step by step diagnosis, It would be much faster than posting the answer to each question on here
chris r, January 2009