Alternative outbound routes

I need an advice.
I need to configure every first and second call to extension 9. to go over trunk1 and every third call to go over alternative trunk2. Can anyone give me an advice how to achieve that

Use a global variable. If the this behaviour is crtical, you will also need the Lock application, which means using at least version 1.6.x.x.

You didn’t say which version you were using.