It's a $30 charge for data for each iPhone you have on your account. Text messaging is $20 for unlimited for a single iPhone or $30 for unlimited for the whole family.
To clarify:
1) A family VOICE plan has voice minutes shared by all, then...
2) Each iPhone 3Gs must have its OWN $30 data, then...
3) You can buy (or not) individual text plans of varying minutes per phone or one blanket unlimited family text for an additional $30
if you use some feature codes that might help. with fan accounts there are codes, used before from other subscribers, that you can get 1500 text for 8.99
So I have a question on something of the lines. I get the whole reason of having the data plan for the 3G. So after the 2 year contract is over and you keep your 3G and use it after the contract is over, can you dump the data plan since it's "paid off"?