I am planning to get iPhone 4S but not sure which data plan is better for me in terms of cost and data use.  AT&T webpage shows the difference of $20.00 between 2 GB and 4GB data plan which I think is big difference for students like me. Can anyone suggest me which data plan should I buy? I will have wifi available most of the time and If I need to download data for somewhere else that will be basically for email checking.  

You just answered your own question !

If you're gonna be on WIFI most of the time, get the 2 GB. It will be more than enough for you.

90% users use less than 2GB of data.

I have 2GB and use facebook, skype, email and WIFI at home. It is enough for me.

Also if you're a student, you'll get 15% discount on AT&T with your .edu address.

Good Luck. .

 aba 2 GB pani kina chahiyo ra afu ta 15 rupaiya ma kaam chalaincha 200 MB. every $ counts for me as a grad student & also iphone pani boknai paryo peer pressure :D.

 4GB is way too more than you probably need. 200 MB will be enough if you don't watch tooooo many videos... . Don't download apps when u are in 3G..

 thanks guys!

Never mind, i found the link of actual data usage calculator

cheers,

http://www.att.com/standalone/data-calculator/index.html?locale=en_US