There are so many options now. You could install Asterisk/FreeSwitch/FreePBX internally and purchase a SIP trunk with unlimited minutes from a provider like Ar

There are so many options now. You could install Asterisk/FreeSwitch/FreePBX internally and purchase a SIP trunk with unlimited minutes from a provider like Aretta (https://www.aretta.com https://www.aretta.com). I personally don't have any experience with them. Or, you could pay to have the provider host your PBX, which will probably save you a ton of work, but will (of course) cost more. http://www.phonebooth.com http://www.phonebooth.com is another option.