Just spitballing here:

Con

Availability: cellular generally covers more area and has a lower threshold for connection

Complexity: speaking as someone who has run asterisk and cisco unity communications at different (VoIP servers), they can be pretty complex to setup and maintain. There are ways to make it simpler, but you still need to have a server somewhere. You'll also want to setup a VPN or similar if running your own VoIP server

Privacy: if you use a third party for the VoIP server (not service) theoretically they can see everyone you call and when

Pro

Customisation, the amount of ways you can configure VoIP systems is incredible, like what ring tone/music a caller hears, how unanswered calls are handled

Reporting, much easier to get reports on how many phone calls, at what time etc (due to logs), could even use something like elk or graphana

Security: Users using the same server can have end to end encryption, and the voice calls can be peer to peer. I.e. after the server iniates the call it goes direct