Other than freePBX, that’s pretty much the way I have my system setup.
So, with your setup you could call between the two phones, but can’t dial out.
If you just want to call random people, you could use iaxtel: http://www.voip-info.org/wiki/view/IAXTel
However, if you actually want to call other phone lines, you need a service that provides termination into the phone system. You have a couple of options:
1 – Get a regular old phone line (POTS/PSTN) and connect it through a FXO interface into your asterisk server.
2 – Get a service that you connect to through the internet to terminate your phone connection. Most helpful if you actually get a phone number with this system.
For asterisk servers, I’ve been really happy with the slihgtly confusingly named teliax. They have a pay-as you go service that only bills you for what you use, and various monthly plans that come with set amounts of minutes. https://teliax.com/ Sadly, they don’t have a referral plan, or I’d give you a code.