Hello, I'm a former VoIP technician, I worked 10 years on the NOC department for a US company, I'm experienced troubleshooting, configuring, securing and customizing all sort of VoIP/SIP equipments and softphones as well as PBX systems such as Asterisk/FPBX; I read your requirements and I can certainly install and configure GoIP on your Asterisk. Please contact me and I'll get this project started for you.
Thank you!