Therapists don't need voice mail messages that demean their patients. I just called a psychotherapist colleague and listened to her voicemail greeting with the now-ubiquitous message, “If this is an emergency, hang up and call 911.” My professional voicemail will never include such a message.
Set the expectation by providing a realistic timeline for when the caller can expect a return call. Remember once the expectation has been made, make sure you follow up and return the call as promised.

While missed calls aren’t ideal, you can let your caller know you’re still there for them by having a great voicemail greeting. The best business voicemail greetings let your customers (and potential customers) know why you’re not available and how they can best get in contact with your business. They are also short and to the point. You usually want to keep your greeting between 6 and 24 seconds long so callers don’t hang up halfway through.
“Hello ____. This is _____ again, calling from ______. I ran across some information on a client who made dozens of offers on houses before someone finally accepted one of them. We learned a lot from the experienced and I successfully used the findings to help other homebuyers make bids that were accepted early in the house hunting process. I thought I would share it with you in hopes of saving you time and making it easier for you to purchase the home of your dreams. I’ll email you the information. Give me a call if you would like to review it together. Thank you.”