Can I use my iPhone data plan on my iPad

How do you mean use your iPhone data plan for a WiFi iPad? Are you thinking of using the iPhone as a mobile hotspot and connecting your iPad via the iPhone? If that is what you want to do the answer should be yes since the iPhone is actually the device providing the data connection.

If you want your phone to act as a mobile wifi hotspot, that involves extra fees with Verizon. I'd assume the same would be true for other providers, but you'd want to talk to your cell service provider to know for sure.

You're right, but I didn't go there since it wasn't clear that was the idea. When Verizon started that program it was $20 a month, not sure what it is now. Unfortunately they did not allow you to go in and out but had to stay in once you started.