[stephenbez]

How is this any better than passwords? 1/10000 chance of guessing correctly is huge.

Why would I want to remember a different passcode every month?

If after two failed login attempts, I must respond to an SMS before I log in, it's really easy to DOS.

Users will be confused by this new scheme. Stick with what has already been vetted in the industry.

[jonalexr]

Yeah that's true, thinking about it further a way to solve this could be allowing infinite sessions with the initial passcode being sent to you via SMS.

This way you wouldn't need to remember a different passcode each month and the login attempt issue wouldn't exist because passcodes are generated when you need to login.