I understand you requirement. So, if any call you your twilio number, then first twilio will say "Welcome to our call center! Please wait until someone is ready to assist you.", After that a hold music will play. Then all of the queue will work according to availability of agent.
Can you please tell me only need to this work or you need more information from twilio regarding the call status report, recording of all calls like that.
You will just go to my profile, I have just finish this job
https://www.freelancer.com/projects/php/build-twilio-predictive-dialer/
So I can do anything from twilio, need what you exactly need in application, that i can estimate the work and deadline.