Go get rid of that sign up form
Weipin Xia

I think this post should be presented more as an alternative to signup forms, as opposed to suggesting we should replace signup forms. I think the number of people who will be willing to give out thier cellphone numbers will be very low (I would never give it out in this context, and I don’t know many who would), and as Dan pointed out, the iCloud option only covers iOS users.

Your updates suggest alternatively using a social network to login such as Facebook, however people are getting more and more hesitant to use Facebook for things like this as Facebook continues to reduce the level of privacy offered to users.

All of these options are great supplements to a signup form if used properly, but replacing it completely with the options you mentioned carries a real risk that you will alienate your users.