I have a fairly good idea whats wrong... as I just had my phone replaced this past weeked for the same reason
My phone like your's just outa the blue started to lock up, loose connection with the memory card OR show the card was there but when you went to access it, it would just sit there and think... then freeze
.
I took my phone in to sprint... after a HARD reset the tech tells me the problem was my memory card adaptor from Micro SD to Mini. So I took it back home, replaced the adaptor with another BRAND new one i had... same thing... took out my wifes Mini SD card and tried it... same thing... call back the tech and he tells me that "it worked here" well it don't for me
. So he tells me he'll set up a reservation for me and look at it again. Back down i goto the sprint store... he looks at it again and finds it does have a problem... that he can't fix. By now I'm a little pissed after nearly 4 hours at the sprint store... I think he sensed this
so he tell me he'll BRB... back he comes with what looks like a BRAND new 6700... the ONLY way I could tell it was a referb was the TINY bit of ware around the mini USB port... other wise not a SINGLE SCRATCH on it
Bottom line... take it in if you have insurance.