Going from HTC One X to iPhone 4

No, switching to an iPhone 4 should not be too much of a hassle for you. You should call customer service and let them know that you need to change your data plan from a regular smartphone data plan to an iPhone-specific data plan. Yes, it kind of seems silly to do so, but it needs to be done so that you can use your iPhone to its full potential.

If your microSIM card is still active, simply pop it into the iPhone once you receive it and you should be good to go.