Hello Prion,
you're right, the UM 423 SIM-Cards can be reached again (since yesterday 5th Nov, evening)
Incoming calls are possible (i did a test-voice-call for round about 1 minute
I cannot say, what's happening there at the moment in detail.
If you like to bet, see to your bet-shop and place a bet on United-Mobile
BTT: I'll try to find out some more stressable news, if possible. Stay tuned.