Re: OS vs apps: Paint
The first iPhone didn't even have 3G, only wifi. So having a data plan was irrelevant.
Once operators saw the uptake and the potential, they were falling over themselves to launch iPhone-specific plans. Also, Apple charged operators a few bob for use of the trademark "iPhone" in their plan names. For a while you could get the exact same plan at a cheaper price by choosing the variant without the fruity trademark in the name.