[Kay]

Most carriers have an automated system that runs and attempts to protect customers on the next available flight. Generall you are contacted when there is a change. Since they are likely dealing with thousands of customer and flights changes they may have an automated system or a live agent call you.
Often times these call are made in date order. So if they have a schedule change 3 months before your scheduled flight, then the customers booked before your travel date will be contacted first.
As for policy all carriers reserve the right to change there schedules. Normally if the there's a schedule change, the customer is offered reprotect on another Carrier or an involuntary refund if what has been offered does not meet your needs.
Try visiting their web site. Check to see if they post the Contract of Carriage rules. Look for the rules regarding flight delays and schedule changes.