AussieMom: I know exactly how you feel...I was in the same boat as you other than the genders were reversed.
What we do now may not be very popular, and I know I didn't like it at all at first, but the kids, the ex, and even myself have seemed to adjust and this is what works best for us now....
If the kids are at their Mom's, I don't call them at all (unless there is something important) but they can call me anytime (they usually don't). My older kids occasionally email/txt or even Facetime me....but even that doesn't happen very often anymore. When the kids are home with me, it's the same. The ex does not call here for them but they know they can call her anytime they want, they just choose not too.
I'm just guessing but I have thought about this, a lot at first too, and I think if you put yourself in the kids shoes, especially if there is quite a difference in what kids can do, how they can behave, etc. in the different households, it's almost like they live 2 different lives and they keep them separate. I got the same thing when I first called any of my kids when they were at their Mom's and it was never a very pleasant phone call. I too didn't really enjoy calling them after awhile and I didn't like the awkward silence we would have. I'd often wonder if they're mother was in earshot and they were afraid to say anything to me (which with my ex, this was *very* possible!), or maybe they got grilled after each call by Mom about what they said, what I said, etc., or maybe I was just interrupting them doing something fun....or worst of all....maybe they were living that part of their life they have there and my calling reminds them of their other life and how Mom & Dad don't live together anymore, etc.
When the kids get home from their Mom's I never ask them about what they did there or who said what or what happened or anything. I usually just tell them I'm glad their home and I may ask if they had fun at Mom's, and that's it. Sometimes they will tell me about something that happened over there but not always. But....shortly after their home everything seems to go back to normal and we talk and joke around and do everything we always did, so it's all good that way!
If you asked me a few months ago I never would believe I'd be saying what I'm about to say, and that's that I've learned to enjoy my time now when the kids are at their Mom's. Don't get me wrong because I'd MUCH rather have them here ALL the time...but since that isn't going to happen, I'm adjusting to the kids spending about 40% of their time at their Mom's and we all seem to be ok going without talking to each other for that time. Unless the kids ask me to change this, I'm going to leave it the way it is and it seems to work.
Oh and this may be relevant too....our temp custody schedule would be something like a 2/2/5, except my ex brings the kids home 1 day earlier on her wknd's (at her request to the judge! her loss, my gain! long story lol) so the longest stretch the kids spend at their Mom's is 4 days every other wknd. If we were doing a week about arrangement (or some other schedule where the kids spend a lot of consecutive time at each parents home) I don't think I'd want to go that long without talking to them.
AussieMum....I really felt compelled to write you though because I really did feel the same as you at first. I felt like I was losing my kids and it was the worst feeling ever....and then I didn't like how awkward it felt to talk to my kids while they were at Mom's. I remember being so angry at the ex and the world in general because I didn't think I was going to be able to do this. So I just wanted to write you and tell you that with time, I've improved so much and the kids seem to be happy with the way we do things now and like I said, to my huge surprise I've even learned to enjoy my "me time" now when the kids are at their Moms. I'm sure with time you'll feel better, and safer about everything too. Hang in there AussieMum :-)