You can work out which kindle you have by looking at first part of the serial number and the list below:
B001 = Kindle 1
B002 = Kindle 2 U.S. (Sprint)
B003 = Kindle 2 International (AT&T)
B004 = Kindle DX U.S.
B005 = Kindle DX International
B006 = Kindle 3 3G + WiFi Graphite/White (U.S. and Canada)
B008 = Kindle 3 WiFi
B009 = Kindle DX Graphite