Can you go a little more in depth about the maintenance contracts you have with customers? Does that mean they get a fixed number of hours of your time every month? What if they go over that time? Does it mean being on call? Thanks.
Create a nice pile of things that have a good value for the customer, and either are easy to automate (like hosting), or likely don't eat to many hours. You'll lose the ability to invoice your customer for the 10 minutes mail or phone help, but you would need more then 10 minutes for book keeping and invoicing of those small things. So better sum them up, if you want to keep contact to a good customer. As funny as it sounds. The annual maintenance invoice was often the starting point for a custom asking me to solve a total different problem.