Does the authorize.net plugin support the SIM api?
This is where the user enters the secure data on
the authorize.net site rather than on your own site.
The forms etc. are managed in the Authorize.net
control panel.
CBSubs 1.0.3 supports Authorize.net AIM (Advanced) and ARB at same time, but not SIM (Simple), as SIM doesn't support auto-recurring billing (ARB) at same time.
Upcoming CBSubs 1.1 will additionally support Authorize.net "silent calls" and AVS as well, but most probably not SIM.
CBSubs 1.1 will also have an API which will allow to more easily add support for many more gateways, possibly Authorize.net SIM too.