Copied from one of your previous posts.
I am on a family plan with a few other iPhone 3Gs, and myself who has an iPhone 3G.
I would like to upgrade to the iPhone 3G S but the other lines do not want to and therefore do not want to renew the contract, forcing me into the no-commit, no-contract price. I am also under 18 and not the primary line on the account.
Your line/number for your iPhone will no longer be under the existing contract for the Family Plan if you go with the no-contract or pay-as-you-go option with your iPhone 3GS purchase.
Since I am keeping this plan and not renewing anything, what am I signing when I buy the no-commit, no-contract iPhone 3G S?
I already answered this with my previous post.
A contract which is an agreement involving payment terms, service, rates, etc. It is a contract, just not a long term contract or annual contract.
I am fairly certain that you will not be able to enter into any agreement with AT&T if you are under 18.
And if your iPhone 3G was purchased at AT&T's subsidized or discounted price, your line/number remains under contract with AT&T under the Family Plan. You cancel the existing contract for the subsidy received for the iPhone 3G and the account holder for the Family plan will be charged an early contract termination fee for your line being cancelled with the Family plan.
You need to contact AT&T - I suggest visiting a local AT&T store to ask if someone under 18 is able to get a no-contract or pay-as-you-go option with AT&T.