S.C.
My son always sucked his fingers-- everyone told me I'd NEVER be able to get him to stop. My PLAN was to make him stop gradually once he got to 2 1/2 or 3, just by telling him every time I saw him with his fingers in his mouth that he must be tired and letting HIM choose either to go to bed to suck his fingers or to take his fingers out of his mouth.
HOWEVER when he was about 2 he had the night from H*LL. He'd put his fingers in his mouth, take them out, look at them like "EWWWW, they have SPIT on them" and then start screaming for awhile until he put his fingers back in his mouth.... I think he did that for like 3 hours (It seemed more like 3 YEARS, I think I was chanting at one point for him to just PLEASE put his fingers in his mouth and Go the ____@____.com to SLEEP!) but he hasn't put his fingers back in his mouth since that night......