there are Dialer Codes for this sort of thing. i used them on my SamsungMoment(RIP) and was able to test the functionality of all parts of the phone.
if you're rooted, or on 2.1 still
## Codes (Programming Codes) Listing and 2.2 Dialing Fix - xda-developers
has a ton of dialer codes that you can use to access menus of your phone.
i was unable to find one specifically for the camera (but i'm froyo, so it doesn't work for me anyways)
but i'll keep looking and post one if i can find one.
might have to go and become friends with a SprintTech
still under that 1yr HTC warranty--so you're covered for a replacement!
UPDATE: some users (via posts) are reporting their camera doesn't work AFTER they recently upgraded their firmware (on 9/23) to remove the FPS cap. this might be a larger issue than just your phone, might want to call Sprint to check.