How do I change the caller-ID that people see when I call them?

You can change the caller-ID that people see when you call them in two ways:

By the contact you call - Each person can see a different caller ID. Click on one your contacts and in the "caller-ID field" choose a phone number you want them to see as your caller-ID when you call them.
Globally - in the "Your Caller-ID" box, choose automatic or manual. If you choose manual, enter the caller-ID that you want people to see when you call through Zenofon. If you leave it as automatic, your real caller-ID will pass through.