Vodafone network outage
We have experienced outages on the Vodafone phone network, which operates the MU staff SIM cards, during the day. Not all users are experiencing the problem, but you will be able to tell by not being able to call the number you want (you may get a "not registered on the network" message) or similarly, other colleagues may not be able to call your number. The outage also affects private numbers under the University's framework contract.
It is relatively easy to resolve the problem by restarting your phone.
A fix is being worked on, thank you for your understanding.