Can the sprint phones be unlocked for use with the Kroger iwireless phones?

The phones and plans in Kroger are with iwireless which goes through sprint network from what I have found out. I really like a phone from Sprint, but I like the plans with kroger because their prepay service is cheaper for me than sprint's prepay. On this website is the info I found so far.... http://www.journalgazette.net/apps/pbcs....

Can the sprint phones be unlocked for use with the Kroger phones or do they maybe have sim cards that can be switched?