How many gb of data do I need for my iPhone?

I'm about to buy an iPhone. I would use the talk and text often but I'm wondering about the Internet data. I know I'd use it when I'm on the bus and at other friends houses. I was wondering how many gb would I use with it on almost constantly and how much would it cost with Verizon wireless.

If you have Wi-Fi around and you can connect to it you won't have to use gb thats what I do anyway. I have 2 gb and I use it away from Wi-Fi a good amount and i have never went over the limit. Mostly just listening to pandora and watching youtube videos or going on the internet.