this was a simple release day problem that was suppose to be fixed by the ota update that pops up soon as you get the phone. if you didnt install the update you may want to now. if its still not working, then it may be time to take a trip to the sprint store already. because you are going to need that memory slot. i think the built in 16 gigs is only useable for the applications.
http://thenextweb.com/mobile/2010/06...y-card-issues/