check out tmobile's forum itself, you'll see people complaining about the same issue. So I printed it out and went to a local tmobile store. Since I told them about the issue, they said they couldn't exchange my phone or do anything, except what the instructions said to do. The instructions were simply to call HTC, which they let me borrow a 2GB card, which for weeks now not a single issue.
When I had the 8GB card I had the exact issue and formated, reset my device...etc and nothing would help, but once I got the 2GB sd card, not a single issue. It started out with camera as well then just random it would ask for my sd card.
The first time I called HTC, the person on the phone took 30 minutes and told me they would ship me a new SD card, but they are out of stock and for me to call back in a week. I called back in a week and the person on the phone told me the first person was crazy and they always had sd cards in stock. She took all my information and shipped it.
There's so many posts on tmobile's site about the issue. I would print them out and go into a tmobile store.
Re: My touch SD issues - T-Mobile Community