1) Your brother 14, a minor, is not competent to make a contract. That alone should make the contact invalid.
I have 2 problems with this whole situation.
First, as pointed out above, a 14 y/o usually cannot enter into a legal contract by themselves. IANAL, but I just took and insurance law course and at least in that industry an insurance policy requires an adult to sign the policy.
A few years back, Cingular sent my wife's aunt and uncle a piece of junk mail advertising their service. They were out of town at the time and someone stole their mail while they were away. The thief used personal info they obtained from the mail he stole to set up a Cingular account in their name. A while later, a bill for $1800 showed up. They disputed it with Cingular, but they wouldn't budge. Since they were in the process of securing a loan for a new home, they relented and paid so as not to affect their credit rating.
How can Cingular hold anyone to a contract if they never signed the contract? I believe with Sprint, a long time ago, they used a 3rd party and recorded my voice when I signed up over the phone... but I'm not sure of that. And if Cingular did do that, then they should've been able to go back to that recording. But still, any of these methods that allows you to enter a contract like this w/o verification are unsettling to me.
Second, what if someone accidentally entered the wrong SSN and it happened to go through. Then you forgot the SSN you incorrectly entered? Are we saying here that at least in that event you could go to the AT&T store to get the mess straightened out?