Mass Mail tool > Product/Service Criteria > Billing Cycle
Currently when mass mailing customers by product, you can address your Email based on the Product/Service - the Status and the assigned sever. There is no way to Email clients based on their products billing cycle.
When Emailing customers concerning price changes, it would be very useful to Email them based on their billing cycle, as the price for only that cycle might be changing. Also, this would be useful if you decide to stop offering quarterly or semi annual cycles for example, - you'd only want to Email those affected instead of everyone.