When a caller says "can I come in Thursday afternoon?", three things have to happen: someone checks the calendar, agrees on a time with the caller, and writes it down where the rest of the office will see it. An AI receptionist can do all three during the call. How well it does them depends almost entirely on the calendar and the rules you give it.
This guide covers booking by phone into Google Calendar or Outlook and Microsoft 365 with ModPhone: how the agent checks availability, what to collect from the caller, how confirmations, cancellations and reschedules work, and the settings that stop it from double-booking you.
How the agent checks availability
When a caller asks for an appointment, the agent works out which appointment type fits, asks for a day and time, and checks. A time counts as available only when three things are true: it falls inside your booking hours for that day, the calendars you selected are free, and nothing already booked through ModPhone overlaps it. If the time is taken, the agent suggests others. Before it books, it reads the exact date and time back and waits for a clear yes. It is instructed to check availability before every booking and never to promise a time it hasn't checked.
Google and Outlook differ in one important way.
With Google Calendar, you tick which calendars count. Any event on any ticked calendar blocks that time, including all-day events and events you marked as "free" in Google. New bookings are written to the first calendar in your saved selection.
With Outlook, availability comes from your Outlook schedule. Time marked Busy, Tentative or Out of office blocks a slot; time marked Free doesn't. New bookings go to the default calendar of the Microsoft account you connected.
You can connect both. A time then has to be free in both calendars to be offered, and confirmed appointments are written to both.
What to set up before you turn booking on
Booking needs three pieces, all under Appointments in the app.
- Connect a calendar. Go to Calendar Settings and connect Google Calendar or Microsoft Outlook. Only the owner of the phone number can connect it. For Google, open Select Calendars and tick every calendar that should block your time.
- Add appointment types. Each has a name, a description, a duration (15 minutes to 2 hours), a buffer after it, and how far ahead it can be booked. The agent uses the name with callers, so call it what callers call it: "New client meeting," not "INTAKE-A." Only active types are offered.
- Set booking hours. Enter the start and end time for each day, and switch off days you don't take appointments. New numbers start at Monday to Friday, 9 to 5. Watch the switch labeled "Offer appointments every day, 9 to 5": while it's on, your day-by-day hours are ignored and weekends are offered too.
Booking hours decide when appointments can happen, not when the agent answers. It keeps answering calls around the clock, so a caller at 9 p.m. can book tomorrow's first slot.
If you book in GoHighLevel rather than Google or Outlook, there's a separate GoHighLevel integration, enabled per account, that books directly into those calendars.
What to collect from the caller
The agent collects what it needs to make the booking: which kind of appointment, the time, and the caller's name. The number they're calling from is recorded automatically, and the confirmation text goes to it. If they give an email address, they get a confirmation email as well, and on Google Calendar they're added to the event as a guest.
Anything else you need, add to the agent's Core Instructions, one rule per line. A few examples:
- A tax office: new or returning client, individual or business return.
- An auto repair shop: year, make and model, what the car is doing, and whether it's drivable. Skip the VIN; 17 characters over the phone is asking for a typo.
- A city permit office: the property address and the type of permit.
- A school office: the student's school and grade, and nothing from the student's record.
Keep the list short. Every extra question is one more chance for a caller to decide this is taking too long.
Confirmations
Right after booking, the caller gets a text with the date, time and service, asking them to reply Y to confirm or C to cancel.
A reply of Y (or YES, or CONFIRM) sends them a confirmation text, and the appointment is added to your Google or Outlook calendar. A reply of C (or CANCEL, N or NO) marks it cancelled and tells them they can call to reschedule. Anything else gets a reminder to reply Y or C.
This is the part people miss: the appointment appears on ModPhone's Appointments screen as soon as it's booked, but it only lands in your Google or Outlook calendar after the caller replies Y. The agent still counts an unconfirmed booking when it checks availability, so nobody else gets that slot. But if your staff work only from Outlook, they won't see it there until it's confirmed.
Landlines can't receive the text, so a caller on a landline can't confirm this way. Glance at the Appointments screen each morning for bookings that are still unconfirmed, and call those people.
Cancellations and reschedules
A caller can cancel by replying C to the confirmation text.
If someone in your office cancels an appointment in ModPhone, it's removed from ModPhone only. The event stays in your Google or Outlook calendar and the customer isn't notified, so delete the calendar event yourself and let them know.
The agent doesn't move an existing appointment to a new time. When a caller phones to reschedule, have it take the details and pass them on. A Core Instructions line does it: "If a caller wants to change an existing appointment, take their name, the current time and the time they'd like instead, and tell them the office will confirm." Your staff then move the event in the calendar. Because the agent reads that calendar, the old slot opens up for the next caller and the new one is blocked.
Keeping it from double-booking
The agent can only avoid conflicts it can see, so the work here is making your calendar accurate. Go through this once before you go live:
- On Google, tick every calendar that holds real commitments, and untick shared or holiday calendars that make you look busy all day.
- On Outlook, make sure blocked time is marked Busy, not Free.
- Put lunch, staff meetings and paperwork time on the calendar as events, so they block time like any appointment.
- Set booking hours to the hours you see people, not the hours the doors are open.
- Every so often, check that the calendar still appears under Connected Calendars. If ModPhone can't reach Google or Microsoft when it checks, it treats the time as open rather than refusing to book, so a lapsed connection is how double-bookings creep in.
- If staff also book by hand, they need to put appointments on the shared calendar as they make them, not at the end of the day.
Then test it: book a slot on one call, and on a second call try to book the same slot.
Common questions
Can an AI receptionist book appointments into Google Calendar?
Yes. ModPhone's agent checks the Google calendars you select, offers open times inside your booking hours, and books during the call. The event is added to your Google Calendar when the caller confirms by replying Y to the text they receive.
Does AI appointment scheduling work with Outlook and Microsoft 365?
Yes. Connect your Microsoft account and the agent reads your Outlook schedule, treating Busy, Tentative and Out of office time as unavailable. Confirmed appointments are written to the default calendar of the connected account. Some organizations require an administrator to approve new apps before the connection works.
Can callers cancel or reschedule by phone?
Partly. Callers cancel by replying C to their confirmation text. The agent doesn't move existing appointments itself, so for a reschedule it takes the details and your staff change the time in your calendar, which the agent then respects for later callers.
Will an AI receptionist double-book me?
Not if your calendar reflects reality. It checks your booking hours, the calendars you selected and the appointments it has already booked before offering any time. If a conflict slips through, check for an unticked calendar, events marked Free in Outlook, or a calendar connection that has lapsed.
Before you switch booking on
Open next week's calendar and ask whether a stranger could tell from it when you're free. If they could, try booking on the live demo. If you're still comparing products, our buyer's checklist covers the questions to ask about calendars and everything else.