I Have successfully deployed and managed call center solutions like Digium Switchvox call center solutions, Aheevaccs call center solution, Asterisk open source solution, Elastix call center solution etc.
I can help you in setting up asterisk server so that we can make free SIP calls via Zoiper. I have good experience in making SIP calling feature. We can also make video calls over Asterisk server. I can handle all custom tones, time out features for Zoiper.