Call Cricket and ask. I wouldn't hold your breath, though. According to this: http://support.apple.com/kb/HT1937?viewlocale=en_US&locale=en_US They are not a supported carrier. I don't know whether Apple's list is out of date, or whether Apple's list is correct and Cricket lost the iPhone.
Cricket's web site does not list the iPhone as an option, though I believe it used to be.