UPDATE After much hoo-haa, I finally got to talk with our son on Sunday. Her phone had died and didn't know it. She apologized ("Sorry sorry! My phone died and didn't realize it."), but that's the reason why I scheduled with her when I would call in the first place -- so she would be READY. I finally got a hold of them on Sunday evening. She had told me that I could call whenever that day, but apparently not. Once again, I tried setting up a time, but all she said was that they might be in an Imax theater. Eventually she called back after I had tried a few times, as well as texted her more time options. Something new she's doing nowadays (whether she calls or I call her phone) - she would immediately pass the phone to our son. Occasionally she would say "Hello?", but never more than that. Not even a bye. That's all done via our son.
On the plus side -- ONE MORE DAY till I see our son! They return today, and I'll be picking him up from daycare tomorrow and it'll be his night with me.