We use a cloud based phone system called phone.com. It'e been very affordable for us. They have a very complete JSON based API and I know you guys could add this in two seconds! Their API covers the full call interaction between the call coming in, being answered, and the call ending. They can do that for outbound calls too. There is also the ability to send and receive text messages through the API.

Phone.com API knowledge base -> https://apidocs.phone.com/docs/account-listeners