well basically a locked phone is altered by the carrier
The benefit of selling an unlocked phone are 1st you get people who like other carriers, pre paid or no contract looking at the phone as well. And 2nd you could sell out of the US (some countries pay more for a phone)
At&T unlocks phones
General Eligibility Requirements for Unlocking iPhone
AT&T will unlock an iPhone under the following circumstances:
- The person requesting the unlock is:
- a current AT&T customer or
- a former AT&T customer who can provide the phone number or account number for the account
- The iPhone was designed for use on AT&T's network;
- All contract obligations, including any term commitment, associated with the device to be unlocked have been fully satisfied; and
- The iPhone has not been reported lost or stolen.
Additional Information about iPhone Unlocks
Current customers will be allowed five (5) unlocks per account, per year, so long as their account is in good standing with no past-due amount or unpaid balance
and has been active for at least sixty (60) days.
Former customers will be allowed five (5) unlocks per former account so long as they owe AT&T no Early Termination Fee or other unpaid balance.
In addition, AT&T will unlock an iPhone for: (i) an active and deployed member of the military who is a current AT&T customer in good standing and is able to provide AT&T with deployment verification; and (ii) a person who purchased the iPhone from an authorized location at the "no commitment" price and can provide proof of purchase.
iPhone Unlock Requests
In order to request iPhone unlock, you should log in to your myAT&T account to
contact us by email or chat. You may also contact AT&T Customer Care at 800-331-0500.