How about going to the web site of the service provider you use..... you can get your answer there.... though not as exciting as starting yet ANOTHER thread of similar topic.
www.att.com
or dial *639#
If you JUST entered in a contract for 2 years, I believe you'd only be eligible for the "early upgrade" price which is, I believe, $300 for the 16gb.
hmmm
I'm gonna set up a new 2 year contract with the origonal iphone so i can get unlimited data plan.....and get it carried over to the iphone 4