I would like to host my own conference calling PBX. However I can’t find a SIP provider that offers unlimited channels and charge by per minutes. Any recommendations?
TIA!
Look at AnveoDirect, Voxbeam, AlcazarNetworks, Flowroute.
If not suitable, please answer:
What country?
Expected number of participants?
Calling in on geographic number?
Calling in on toll-free number?
Calling out to participants?
Why do the commercial services not meet your needs?
We are using SIPBound for our Amazon-hosted PBX in the USA for US/CAN calls, as well as GB/PH calls. They also have dedicated servers (hosting division is called CloudSouth) at decent prices. The customer service has been nothing short of phenomenal over the years. Since we pay per minute, they’re willing to set us up with as many ways to spend money as possible! 
Thanks Stewart1 and Overkill. We are currently using Level3 as our conference calls provider and getting charge $0.20 / min / person, a bit pricey. I will review the list of companies you recommended and see how that will pan out.
VoipInnovations (in spite of their recent spate of DDOS problems) has always been good to me. I also use Alcazar as my backup for outbound.
Both of these charge by the “connect unit” (think 6-10 units per minute) and, as far as I know, only limit you to the amount of network you can use.
The phrase “Unlimited” is pretty challenging - you are going to have to use inbound and outbound bandwidth, so your network may well be the limiting factor on unlimited connections.