I have found this occuring a little more often over recent months too.
Primarily in certain areas where our TPG/vodaphone mobile network signal is often not strong, i.e. in & around the NSW 2428 & 2290 postcodes, among other areas.
It's suspected that Vodaphone's infrastructure (mobile phone transmission towers & transmitters) cannot cope with increased load due to increased customers via downstream companies like TPG over recent years, and hope that they will address this as a matter or urgency.
In our case rebooting phones, turning airplane mode on/off, moving outside buildings etc. often helps.
