Whoa, that's not good your phone constantly reboots when a SD card in inserted. I could not find any known issues or other cases like this. Were you able to go into a Sprint Service and Repair center as fireguy_6364 recommended? Having a tech diagnose the phone hands on would be best.
Sprint Social Care
take the phone and the SD cards into a repair store. this is something they will need to test and see what is going on. i have heard of a couple issue with the sd card but nothing that has caused the phone to go into a boot loop.
This has happened with two SD cards. One Samsung 16 gb micro sd, and a Lexar 32 gb micro sd. It'll work for a while, maybe a month, then it'll just break or something. I was sure to mount the sd cards when I put them in and I never pulled either of them out without unmounting first. The first time this happened was with the Samsung. I unlocked my phone and scrolled through my apps and my phone turned off without the shutdown screen. It just blinked off and then nothing. It began to start up a couple seconds later, then it stopped and tried again. Over. And over. And over. I finally had to take the battery out. I put it back in thinking maybe it was just a random error, but it kept doing it. I took the SD card out and it immediately started up like everything was fine. I figured my SD card was just a bad one and I got the Lexar with more space. I put some music onto this one, and everything seemed fine for a while until the music player started saying it couldn't play this type of file. All of my music was in mp3 format and had been playing perfectly up until that point. The same day, I was browsing through the app store and downloaded something. As soon as it started to install, the phone did the restart thing again. That's two expensive SD cards I've been through. I don't think both could have had something wrong with them when I bought them. Is there something wrong with my phone?
If my phone ruined the SD cards, I think I should get some compensation.