A few reports of this today.
Seems there is a problem effecting a few customers.
Try removing SIM card and rebooting to see if it helps.
The issue mentioned above by @MI5 and @jonsie has been fixed for the small proportion of customers who may have been experiencing difficulty when using voice over 4G and voice over wifi service to make an outgoing call yesterday. We apologise for any inconvenience that this might have caused.
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