The building blocks
Speech recognition turns audio into text. A language model, given your instructions and knowledge base, works out the response and any actions, such as checking a calendar. Text-to-speech speaks the answer. Telephony connects it all to your phone number. Good systems keep the delay short enough that the conversation feels natural and let callers interrupt.
Inbound and outbound uses
Inbound: answering calls, booking, routing and after-hours cover. Outbound: appointment reminders, follow-up on enquiries that came in by form, and collecting simple information. Outbound calling to people who have not given consent raises PDPA and Do Not Call Registry obligations, so check the rules before any outbound campaign.