Spent a week in the BVI's a few years back, but did scout out the fishing. Bottom line is if you're looking for bones, Tortola is not the place. Very few flats. The terrain by the ocean is rather steep, and the few flats we found were 4-8 feet deep.
Same goes for Virgin Gorda, except this island is so beautiful it almost makes you forget about fishing.(BTW my girlfriend and I found Virgin Gorda much nicer, smaller, more fun than Tortola.
Anegada, a small island about 60 miles from Tortola does have 3 big flats and pretty good bonefishing. I got a guide from the Anegada Reef Hotel, and also did a bit of wading on my own, and caught a few good bones.To my knowledge, this is the only real flats fishing in the BVI's.