[dudul]

Note that I believe it is now impossible to sign up for twitter without giving away your phone number.

[MereInterest]

As of a few months ago, it is possible to make an account, but it cannot use the API unless you give a phone number. Since that is what I wanted to try out, I backed off after learning that and so I don't know if there are any other limitations.

[ttt0]

Last time I checked it was possible, but they will lock your account after a day or so until you verify the account with your phone number.

[dudul]

I checked just before writing my message and phone verification was required before even picking a username and password.