Did you contact your carrier to find out the real issue?
Please do not double post. http://www.blackberryforums.com/smar...martphone.html
There is no BB 3800. Is it an 8300 perhaps?
There could be a couple different problems. First, it could be locked to another carrier. What carrier name is on the cover? If that is the case, then you would need to get an unlock code. Not sure what that would cost however.
Second, it could have been reported as lost or stolen or the previous owner's account is in arrears. If that is the case, then you have a pretty paperweight.