Hi!
I ran into the same problems! But it was not any problem of the Release 8.0 or 7.3
The main innovation of 8.0 are only the push notifications via CallKit to Apple devices.
My first problem was: If any User was defined as Multi-Device User, the MD Group was NOT created in MiVb automatically.
So i had to add a Multidevice Group first.
Well, the Decives was now applicable in "my ring group" but i was still unable to pick up the call on my mobile (only the red button) (The strange thig: In MiCollab Web Client - everything worked fine)
After some trial&error hours I was looking on AMC Server, and I was wondering about the "AMC Known IP Adress"
So my Firewall-Guy did not set the IP Adress to 1:1 NAT in DMZ (MiCollab with Webproxy in DMZ)
After setting all the traffic in & out through that specific DMZ Port everything worked fine!!! But who cares, it took only a few hours to find any hint
PS: Micollab Web is working over WebRTC, so the Communication is quite different to MiCollab Mobile
PLUG n PRAY