I bet verizon likes you as a customer. I don't think they will do anything if you call them except offer to downgrade your data plan. You can try though.
Why don't you just go prepaid (page plus for verizon prepaid). $30/mo 1200 min, 3000 text, 100mb of data. Could be less if you buy refills online. Or they also have $55/mo for unlimited talk, text, and 1gb of data.
https://www.pagepluscellular.com/online store/minutes.aspx
It seems like a bit of hassle and might not even be possible to activate a iPhone 4 on pageplus though.
Or go to att prepaid with the iphone. It is easier to get working.
I use about 1.5gb on average on my iPhone 4 on straight talk.