limiting new account registrations
jsz0: SMS isn't a very good solution. Only slightly better than a simple e-mail verification. There are a number of services that would allow someone to receive texts on unique phone numbers. I'm assuming you have a good reason to limit accounts which means inevitably someone thinks they have a good reason to get around your limit.This might be a silly suggestion but I would prefer, as a user, to be asked to submit a photograph of myself holding up a sign with some unique keyword you generate when the user attempts to signup. I honestly think this is less off putting than exchanging CC information. Depending what type of site you're doing it could actually be a fun mysterious way to promote it.