Effect of not calling Sarah
At the beginning of the game, when you arrive on 4th Echelon, there is a phone where you can call your daughter Sarah. After this there is an info box that say you can call Sarah after each mission that you go on, to keep in touch.
What happens if you don't call Sarah during the game?
Solution 1:
According to this discussion here on the Steam forums, it has absolutely no effect. It's just another feature they added to develop the characters a little more.