Online syncronised calander program

I am looking for a program that allows me to get people at different shops book in appointmnts for me. They will all be able to log on with their individual access code and book the diary. I will be able to log on from my office and see what I have for the day/ week/ month.

I want to be able to generate radom access codes to new remote staff wanting the service,

I want to be able to charge a monthly fee for the subscription and if the payment doesnt work I want to service to stop until it is paid,

I want it all the be streamline and not require human intervention only to log on to check diary or to log on and post appointment.

Perhaps make it in to a iphone app?