Help on iPhone plan.

[Bettermann09]

So my mom has T-Mobile and my dad has AT&T and I am currently on the T-Mobile family plan. With the release of the new iPhone I am interesting in purchasing one and joining my dad's plan. I want to have my dad convert his plan to a family plan and I would pay the $30 difference for the 3G data. Would this work or do I need the iPhone specific plan with the minutes included?

Sorry if this has been posted already!!

Thanks:D