Here is all the information about the iphone and what you were looking for http://community.sprint.com/baw/community/sprintblogs/announcements/blog/2011/10/06/sprint-boasts-only-unlimited-data-experience-on-iphone
Dark_Emerald_89 iPhone 4 is available with 8GB and iPhone 4S will be available with 16GB model, 32GB model and 64GB model. Please visit this URL http://www.sprint.com/landings/iphone/index.html?ECID=vanity:iphone.
Hope this helps.
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