First let us say, while there are many blogs discussing the ways to fix VoIP, it just is not true. Think of it as trying to self diagnose a medical condition. It's just not going to happen unless you visit the doctor, or in our case, the doctor comes to you.
Services include but not limited to:
Auto attendant configuration
SIP Trunk Provider setup
Inbound / Outbound route configuration
Dialing Plans and Translations