Calling creatives is hard.
Usually, they don't pick up. So you have to keep phoning and phoning. It's no good leaving a message - no one ever calls back.
And when you do get through, it's awkward. Most creative people are introverts. They don't give good phone.
So forget calling.
Simply send an e-mail to the team you would like to see, explaining who you are.
Why not personalise it a bit? E.g. if writing to Juan Cabral, you could start with "loved your Sony 'Balls' ad".
Other than that, the only trick is to approach an agency as you would a ladder. Start with the bottom rung, and climb.
So see the junior teams first. They're normally easier to see anyway. They won't be able to give you a job or a placement, but they will give you lots of advice. Find the ones whose advice you find useful, and go back and see them again and again.
Only when the junior/middleweight teams like your book, ask who is in charge of bringing in teams for placements/ freelance/ hiring (not before, you'll sound pushy). Then make an appointment to see them.
You'll rarely if ever be able to get an appointment to see a creative director. But that's ok. You don't need to. See a senior team and get them on your side, and they'll pass your book on to the CD.
Have multiple copies of your book. That way, if one gets 'stuck' in some CD's office you still have another one (or two) to take round.
Yes, I know it sounds American, but the fact is they're not just looking at a book, they're looking at two people.
It's probably no coincidence that in a galaxy far, far away, a long long time ago, the first people to give me and Nick a placement (thankyou, Richard & Markham) were two guys that we happened to get on with.