The answer can be involved. Basically, if the contract from the previous
owner was not fully paid off, the phone will not be permitted to be
re-activated. The ID code of the phone is suspended by their system, until
someone goes in to their system and clears it.
The second main thing that stops a phone from being activated, is that its
firmware code set has to be compatible to the service provider's system.
This code set has to do with the type of encryptions, and frequency
allocation groups. This category is the main part that allows to have many
phone providers working in the same areas, and the user phones do not cross
over to other services or interfere with each other. The 611, 0, and 911
services however, are universally compatible, and this is one reason why the
phone can dial these.
This is the reason why you must only purchase a used or new phone that is
intended for the service provider that you are going to be activated with.
Before purchasing the phone, it is best to get the ID, and serial numbers
for the phone, and call the service provider to ask if they can and will
activate that phone.
Now you have the task to get back to the seller of the phone, explain your
problem, and fight to get your money back, if the will return it to you.
For all this trouble is it really worth to buy a used phone like this? With
many of the providers they have basic contract plans where you can have a
phone that is included, and at the same time, you get a full one year
warranty with the phone. Even with a used phone, you still have to buy a
basic plan to use it. The phone that they give with the plan will be a
current model, where you can buy options for it like the carrying case, and
the earpiece for it. Once the model is more than a year out of production,
the options are usually very difficult to find.