You could take a photo, send it to yourself, and delete it immediately. If you got caught taking a photo that you shouldn't be taking, then you could delete it, come up with some bs story "I was texting someone" and there wouldn't be any immediate evidence to contradict it. It's unlikely that anyone would take it any further - a judge would laugh at any attempt to gain a search warrant.

Contrast that with a small camera. Presumably someone who'd want to take such photos would want to keep them. That entails keeping images on the memory. Sure, most cameras have a 'format' utility, but it isn't necessarily easy to use one-handed whilst on the run from an irate victim. And you're out of bs excuses too - there's only one thing that you're likely to be doing when pointing a camera at someone.

That being said, the number of digital cameras taken into public changing rooms etc. is probably 10 times the number of camera phones, if not more. Parents take cameras to swim meets etc. And I doubt that many perverts really think through the pros/cons of which method to use. Heck, half of them are probably getting off on the risk factor anyway. So laws/regulations dealing specifically with phones are probably not very useful. What's next? Banning gameboys because someone might be using a camera attachment whilst pretending to play a game? Better to make regulations that are 'device independant', ie "No imaging equipment in changing rooms"...