When I was first building out my new company with my business partner, we'd just hop on Skype and cover whatever. Now, before I call, I think about what the most important things are and make a list. If it's a very short chat, I send him the agenda in advance so he can fill in anything he needs to cover too.
Man, the difference between how much ground you can cover with an agenda, and how much you do talking about random topics is lightyears apart. So, so much more ground can be covered with an agenda.
You're not bound or shackled to it. Sometimes other things come up, and you roll with it. But having a general roadmap in front of you means if you start the call by swapping stories and realize 30 minutes have passed and you only have 30 minute, you burn fast to cover everything on the list.
When you get off an a tangent, it's very easy to come back around and say, "Okay, cool, so about the brochures..."
I've started doing it for my casual, social calls too. It might sound like it'd be stifling, but it's just the opposite. It's liberating. You know everything you could really enjoy and get a lot out of covering, and you also know when the call is over. Once you've covered everything on the agenda, you say, "Okay, cool, anything else interesting going on on your end?" If yes, you chat through that. If no, then it's goodbye.
I heard on an audiobook recently that some silly high percent of top salesmen have agendas and roughly set presentations before going into meetings. Something like 90%+ of the top 10% of salesmen use agendas. I understand why - if left to chance, you'll probably fumble through nonsense and waste everyone's time.
So, I heartily recommend you set agendas. I'm starting to do this with every business call, every presentation or business meeting, and more than half the social calls I make. Even calling my family back in the States I've started sketching out a rough list of topics before calling, and it's cool to cover like 10 important things in an hour instead of just talking about boring stuff like what food we've eaten recently.
Don't worry about making it perfect. You can just write down 3-5 things on a napkin or sheet of scratch paper before calling. At first it's kind of tricky to sort out your thoughts and decide what's actually important, but don't stress out about it. Just start. Sketch out some things you think would be good to cover the next time you're going to have a call or meeting. It's amazing. I wish I'd known this years ago. Try it before your next call - you're going to be blown away by how much you ground you cover.