Asterisk Live Voice / VoiceMail Detection

What I need done: We have a voiceblast product that needs to have voicemail detection so that we can accomplish two things: 1. When we make a call and it goes to voicemail we need to wait until after the beep then leave the pre-recorded message 2. when a live person picks up plays message with NO DELAY to the user. What I already have versus what the provider will build: we have everything in place all we need is the code for voice mail and live person detection, we have attempted to do this and still are working on it but the options available like WAITFORSILENCE etc.. cause either a delay in a live person experience or for us to miss the voicemail completely. Specific expertise that I am seeking: counseling on asterisk and voicemail detection. Timeframe for delivery: ASAP