I have this issue with my pinkie toe... it likes to curl under my other toes. Especially when I wear close-toed shoes. Since I live in the Extreme Weather Land that is Ohio, open-toed shoes are only an option a few months out of the year. I tried to solve this problem a few years ago by "re-training" my toes with that little foamy toe seperator you use for pedicures. It worked for a few days but then I lost one of the toe seperators and the other one fell apart, so I gave up. I eventually got new ones but they were cheap and didn't help at all. But I think this might be the answer to my toe's prayers:
Yoga Toes ® Toe Trainers