Build a VOIP Solution

I know absolutely nothing about VOIP (apart from what it is ....) so please bear with me ... In essence, I would like to create something like Skype. It would need to accept voice calls, video calls and messaging worldwide. It would need to incorporate billing, so, would need online management. I'm also aware of the dreaded latency, packet loss and jitter. Can this be bridged by a dedicated circuit? .... although people connecting will be using 'standard' internet connections .. broadband etc. Is it possible for people to connect somewhere that isn't 'public internet'. Apologies if any of these points sound positively foolish, I'm just trying to get my head around how this could work. I'm sure it can and maybe to any of you may not seem that complicated .... I'm certainly hoping so. Any advice and mehod for working between us is really appreciated. Many thanks in advance.