Good morning,
swiss news portal 2lounge.ch shows a comment, telling, that Mobilkom of Liechtenstein has taken over the technical platform of UM 423 (United-Mobile) and wants to continue the service by themselves. The "insider" advises to keep the UM423 in a safe place or to insert it in a mobile phone.
See
2lounge Blog Archive Amtlich: United Mobile Konkurs / United Mobile bankruptcy (newer comments on top of the page) in german language.
My SIM card and the Voice Mail are still alive.