Is the emergency lift telephone mandatory?

We have to upgrade our elevator phone from analog to UMTS by the end of the year. Are we obliged to do this or can the owners also vote to do without the elevator phone? What is the legal situation?

or can the owners also vote that we do without the lift phone? What does the law say about this?

In Germany, the majority vote of a condominium owners' meeting certainly does not override building regulations, probably not in Switzerland either. If there is a concierge apartment, the emergency call may not have to go externally, but that is not my area of expertise. Basically, the implementation of the modems used in this regard on GSM/UMTS is not rocket science.

There is certainly an adapter to make the old telephone switching system IP-capable. This is now standard.

there is certainly an adapter so that the old telephone dial system becomes IP-capable.

Lift phones rather operate at main connections, where the dial module is more likely to be replaced than adapted. UMTS is also the more common standard than fixed-line all-IP.