The PSTN is the legacy global phone network built on copper wires and circuit switching. For a century it carried every landline call by opening a dedicated circuit between two phones for the duration of the call.
VoIP largely replaced the PSTN for business by sending calls as data over the internet. Most providers still connect to the PSTN so VoIP numbers can reach traditional landlines and mobiles.
Frontdesk gives you a business number answered by an AI receptionist that picks up every call, qualifies the caller, books the appointment, and logs the whole conversation to your CRM.