According to here
<click here for link>
You have to go to Apple's support to have them increase your device's account limit by 1 so a new account can be associated with it.
You also need to have them re-associate your phone into your account so that it is no longer listed under the previous owner's devices.
Copy pasta from the thread:
I had to arrange an Apple Support call. The Apple Support Team first changed the device to be registered to myself (it was registered to the previous owner).
It now shows up in my devices when logged into Apple Support website.
I was then referred me to Apple Account Security who in turn escalated the issue to Engineering Support, for an engineer to increase the limit on my device by 1, allowing it to be registered with my Apple ID.
The whole process only took a few days.
They said this would now need to be done every time the device needs to be registered with a new user.
-- edited by biggyeyes on Sep 08 2014, 02:45 PM