My ex-boss, who I stopped working for last week, keeps calling me with random questions about the office.?

Well, today he called again, but instead of having the courtesty to leave a voicemail, i think he used the ';page'; function on my phone, because afterwards I got a strange text message with his number on it. I feel like that was very rude of him! First of all, I'd like to have the ability to know what he's calling about before I call him back, and secondly, my phone is NOT a pager, and I feel like he should know that. What should I do? Call him back, or wait til he can at least wise up and leave a message?