Install an IP PBX that can accessed by multiple people aroun

Hello All, this is probably an easy question for all of you.
I want an ip pbx that i can use an ip phone or adapter such as Linksys PAP2T so i and the rest of my friends can connect to it from anywhere in the world. I have access to leased line and public IPs or maybe host it in datacenter. I don’t really understand the technology or the terminology behind IP/voip/SIP PBX.
later on I want to connect a couple of land-lines to the PBX so i can use them when i connect with my ip phone/adapter.
can someone give me the basic idea with the right terminology … I’m ok with the rest of the IT technology but i need a push into the IP telephony.

thanks in Advance

This is very common and in-fact one of the key feature of using IP PBX to make it available where ever you want.
Now there are two options

  1. Through Public IP - Not recommended as you must take care of security unless you are not aware of essential security techniques its not advisable to put your server on Public.

  2. VPN: This is the most common and a secure way. All you need to have a VPN solution deploy on your network and then can register your sip phone with your asterisk servers and start using it.