There are really two options.
1) do not buy the phone (now but perhaps later when your dad says you can)
2) buy the phone and deal with the consequences.
An often used phrase is that it's easier to give forgiveness than it is to give permission.
Perhaps your biggest problem (now) is that you pursued it too much instead of asking once and then buying it anyway. Or just buying it without asking altogether.
I'm not advocating going against your father. But like with anything you will face in life - there are ALWAYS options. We sometimes just don't like them![]()
HE could get his dad drunk and ask then drive straight to the AT&T store(op can drive i assume) and make him sign the contract.