First u need to know how big u wanna be. Then who is ur audience, and how they will make the call
Lets say they use a CPE, like a ATA, so this we enable to use SIP, since its easier than H323.
So we need a SIP server, surf a little u will find out. Set it up. Now the ATA sends message to server, it gets authenticated.
Now we need to be able to pass the traffic to a PSTN node, here the problem, u need to either plugin PSTN lines into ur network, for local calls, or hand over to large IP carrier, or build ur own worldwide coverage..if u have the money come and hire me 🙂
Lets assume u wanna do it in the middle. Pick up the phone call a few large Voip carrier tell em u wanna pass sip traffic, tell em how much, they give u the rates and voila we go live.
If u wanna do it on ur own locally and cheap, get urself asterisk, get a few digium cards, stack the boxes, plugin the pstn lines, build a billing systems, and ur done.
Oh remember people who wanna to VoiP–voip they will only be able to talk to others on ur network, unless u interconnect with other voip providers, which again is easy.
Prozac—-high on life