If you have a customer who wants to be notified when the team is on the way, this Maid Central video will show you how to add that notification type for them.
You'll do this from the Customer level of the account. Click the Contacts tab and click create notification. You'll select the type of on the way notification they'd like to receive, (in this example we set up an on the way text notification) and then click and save the newly created notification. A customer can also set up notifications from their customer portal.