BT have confirmed that an error at their end meant that the transition to the new cloud system – planned for tomorrow – was started yesterday.
They have now corrected this issue but they cannot fix the ad-hoc issues with calls not getting through.
It appears to particularly affect BT mobiles and BT digital lines and so, if you call and it doesn’t connect, try a different phone if you can.
The problem will be fixed tomorrow when the new system is in.
We are so sorry for the problems it has caused.