Beneath all things you actually can do, which I am sure are restricted, I mean, beneath Internet, Postals and Phone, there is nothing else you can really use to communicate with each other on this distances.
I want to empathize here more on another point:
- I was as child often alone with either my mamma(!) :) or my dad.
One of both always was "abroad" working. As child, I did not feel the absence of my father that much as the absence of my mother. First did actually not even really bother me, while second was almost insupportable.
This will be different form child to child, but I think, who suffered the most back then, where actually my parents, not me. Children forget and focus elsewhere very fast.
So, since there is not much you can do, I would rather ask myself, how the child is feeling about and what are the consequences for the child (probably way less painful then for you personally)
- Since your situation seems to be temporarily, I think (specially begin the child 4 years old), you can't really do much here, but perhaps you can pay up afterwards. I am saying this in the sense, that it was for me way more important to have my parents around and "communicative" as "real" persons, instead of phone or Skype calls (which we of course did not have back then)
To "ease" your own thoughts and feelings, I suggest the same as the child does to solve it: Distraction.
the more you think about this situation, the more painful it becomes. The more you distract you with something, it can actually even be something you do for the child, like, who knows, build him a little Playground out in the garden (sorry, I don't know where and how you live...) can distract yourself enough and give a feeling of closeness, which, I am sure, the child feels even if 1000 of miles away from you.
We humans try to always "materialize" communication, while I am sure, specially childs have great working other kind of "sensors"....