Hi Carsten,
Our company tried hosting our own Jitsi Meet server a couple of years ago and it actually worked, but we were having many intermittent problems and in the end decided that hosting video solutions is not our specialty.
We sometimes use the free meet.jit.si instance, but we'd be happy to have access to a paid service if it works well. Currently we pay for many-user rooms at whereby.com, but that is not free software AFAIK.
Disclaimer: I am employed by 8x8.
While it is neither plain Jitsi Meet (it might have some proprietary bits mixed in), nor paid, this service is backed by the company employing most if not all of the Jitsi team members so indirectly you would be supporting Jitsi development as well:
details here (I think dial-in by phone and screen-sharing is included):
https://www.8x8.com/products/video-conferencing
They might be offering paid support for it. I don't know for sure.
Regards, Ion Savin