Dropping to lower plan on Optus biz contract?

With both lower call rates and free "back to base" calls to specified
landlines our monthly bill is a hell of a lot lower than we expected
when we signed new contracts a couple of months ago. This month we
only had $12 worth of charged calls on an $80/mo committment for 2
mobile plans.

What options are there for moving to a lower plan? If we're going to
be wasting $50-$60 a month for the remaining 20 months of our contract
then it may even be worth paying the cancellation fee on one of the
services, which would be offset by the Business Bonus Credit (BYO
handset) on a new contract.

Called Optus but after 2 minutes of fooling around with their infernal
voice recognition system it then decided to let me know they were
closed.

TIA...