All minimum requirements per the road map are complete for beta status. The Multi-Factor module is now a set of core features and hooks and the included module Multi-Factor Call implements these hooks to provide multi-factor authentication.
This release has a stable but unpolished version of multi-factor pin authentication. It was built against VoIP Drupal 6.x-1.0-beta6 and the corresponding Tropo driver.
It may or may not work with other VoIP drivers as I haven't tested them. Please feel free to provide feedback if they work.
