Ben_chmieleski,
Your iPhone is covered by a one-year Apple Hardware Warranty.
In most cases, retailers can provide a duplicate receipt for electronic equipment. That is usually only an issue if the product has not been registered. Registration with Apple occurs during the activation process.
You can check the status of your products registration, and time remaining on the warranty by entering your serial number in the bottom left hand corner of
http://www.apple.com/support/
Hope this helps,
Nathan C.