Before you just pick up a phone and call an agent to discuss representation, the very first thing you should do is visit and spend time on their web site. You might learn that calling them is not something they ask or want you to do. The web site normally makes it very clear how the agency wants actors and models to get in touch with them.
Some agents:
Only want you to upload photos on their web site.
Offer open calls where they meet new people in person.
Request that you mail your head shot/resume or comp card to them. (This is not the norm anymore)
If they do ask you to call them, I would simply ask them what they want you to do in order to talk about getting representation with them.