I agree with K....Don't leave a VM if he isn't there, or if you feel you have to, leave a short one as K suggested. The best thing would be for you to speak to him directly and to say it would be great to catch up....
In terms of how to actually speak to him, I would treat him as as good friend- be friendly and happy- your usual self I believe! Don't be nervous- there's no need to be; you've been preparing for ages, and you're ready.......also, success or failure won't depend on this one call- low expectations and baby steps remember. I think you're going to do brilliantly T!
L.xx
Walk on, walk on, with hope in your heart. And you'll never walk alone.