There are literally hundreds of different call providers to choose from (sometimes called ITSPs) and choosing one can seem daunting. The good news is that any provider that supports SIP should work with Asterisk.
The only difficulty is some providers don’t publish details on using their service with Asterisk. If you’re thinking of using a provider ask if they have details for using their service with Asterisk – it’s also a good opportunity to test out their support!
Here I’m going to use Localphone but the process is usually similar with other providers. You sign up for an account, deposit some pre-paid balance, configure FreePBX then start making calls. This is for outbound calls.
If you want to receive inbound calls you will need to purchase an inbound number. This could be a number in (nearly) an country. You should check out how calls to this number are charged. Many numbers where you pay a monthly fee include a fixed number of minutes and concurrent calls.
1 – Sign up for an account
2 – Add some call credit to your account
3 – Purchase an inbound number if you want to test inbound calls
Set the number so that it forwards to your Internet Phone SIP (this will be your connected FreePBX system)
You should now set up your Trunk in FreePBX