There is a voice maintenance period on Dec 26 22:00 to Dec 03:00. There may be a period of 1 minute where PSTN service incoming and outgoing will be unavailable. If that is the case, please hang up, wait 1 minute and then make the call again.
The time period of this outage will be selected between 22:00 and 03:00 when there is a period of no active calls so impact is minimized.