Become a VoIP phone provider

I am thinking to become a VoIP phone provider, I have 2 years experience with Asterisk , Elastix , Tirxbox VoIPswitch servers, but I want know what PBX system VoIP phone providers commonly using?

none of those would scale well enough - depending on what you want to do. Broadsoft make an ISP scale voip platform but you going to need to save your pennies.