We pay monthly to a specific VOIP provider.
We also pay monthly to a specific Internet provider, without which VOIP would not work.
Buy your own VoIP server and phones. Pay a pro to set it up.
Then pay $30/month for each access line to your local phone company. Figure about 7 people per access line (but two minimum), then adjust the mix as you get data from the phone company.
Your local phone company MAY even have their own VoIP gateway and all you’ll need is to buy their internet service.
In ALL cases get your dial tone from your local phone company.
I’ve been in this field of networks/voip since before there was voip. But I have managed the implementation of VoIP, Internet Access and intra Corporate networks for over 40 years.
You just got some free, but very valuable advice.