AFAIK, texting works with the Sprint SIM, however, you're limited to the network you're roaming on (if X cell company isn't equipped for SMS, you won't be able to text, however, if the network is equipped, you can text and you just pay the SMS roaming fee).
Have you seen these threads:
http://forum.ppcgeeks.com/showthread.php?t=86751
http://forum.ppcgeeks.com/showthread.php?t=87113