Hi Buddy!
I usually write down a 'draft' of telephone conversation if it's about something important or what I'm not used to... Then I use it as a 'springboard' for asking things, you can improvise too, it's good to have some notes to use if necessary.. (I also do that for doctor visits or such, very helpful).
First I write my 'intention' for the phone call or RL conversation - what is it you want to accomplish with it?
If fretting about it, I also sometimes write down what I fret about or 'worst case scenarios', and then brainstorm on ways to avoid those things or get better outcome, or write 'best case' scenarios and realize the reality is usually inbetween.
So, first I would ask you do they usually call you or do you call them, or is it once you, next time they? Do you have some sort of schedule or is it just random? Calling three kids every day might be a bit much for me, and I don't like unexpected calls much either.. I prefer to sort of talk online, or know when we will talk so I can prepare mentally..
Is the time appropriate for you? Just asking cause it can be different time zones. I also have a friend who has often called at very inappropriate times (like lunch time, or when she was cranky and hungry).. Is the time appropriate for them? If not sure, ask.
If I'm hungry and/or cranky I don't like to talk on the phone, and if other people are, usually the same
That friend has a schedule when she goes running and gets more relaxed and it's much less stressful to talk to her after that.
So if they have some sort of routine in the evening, putting kids to bed etc, it might be better to talk when they have time and are relaxed..
Also, if they or you watch a favorite TV show, it may be better to talk at another time.. You could specifically talk about these things and set up some good outlines how and when to call...
So the first thing to say could be, Hi, how are you? Is this a good time to talk/am I interrupting something? and agree to talk later/at another time if needed..
Then you could say 'How's it going?' and see what they have to say... If they have kids, you could ask about those, if they don't, don't bring the subject up!
Also 'no-no's' would be talking about soap operas or crime shows you watched or 'are watching now' (my Grandma does this, lol!) unless they're fascinated with those.. Or it's very exotic or interesting or related to their interests somewhat.
Do you know what your kids' favorite topics or interests or goals/wishes are? If one likes horses, you can talk about the horses.. If one is into eco things, you could mention what you saw on the topic on TV or online the other day..
Also another thing, with the 'empty nest' syndrome many women may feel 'empty', especially if their whole life was around the kids.. So it's really important you take up some hobbies or charity work or interesting stuff you always wanted to do or learn.. This will make you happier and more interesting too.. And if you do cool projects together with your group, you'll have stuff to talk about too..
My Grandma started writing poetry when she was retired already! And she went for trips with the elderly and at times partied more than I did!
A friend's mom is with a painters' club and some women here are with 'herbal club' and there is a 'University for 3rd life era' or something like that, with cool classes on lots of interesting things!
In UK, I saw some people were museum volunteers etc. Lots of cool stuff to choose from!