My T works in an office building with a front desk that handles calls for multiple different businesses. So, when I call her office, I just ask for my T and am put through to her office phone. She doesn't have an assistant and handles all calls and scheduling herself. Fortunately, she's very prompt about returning calls. I have a standing appointment time with her, but if I need to reschedule, we take care of that at the beginning or end of a session. If I realize I need to reschedule on short notice or want an extra appointment, I just call T and we work it out. Usually, I'll leave her a message and if she doesn't have time to return the call, she'll text me with her openings and I'll text back with which time works for me.