'Operator' refers to an operator column in the Appointments page. Therefore if you require one appointment column, then you will go for the 'Single Package'.
There are no contracts, so you can stop at anytime, and there is no cancellation fee.
There is no sign up fee, you only pay an affordable monthly fee, see below for details:
Single Package (1 Operator) - $19 per month
Standard Package (2-3 Operators) - $49 per month
Unlimited Package (Unlimited Operators - 4 or more) - $99 per month