It sucks you've run into an issue :( Everything works fine for me, so it's really hard to help if things go wrong for other people without getting a lot of details. I also know people who have played through the whole game and not encountered any problems with calls, so the calls do work for most people as far as I'm aware. It's just a case of trying to find out why they're not working for you.
Which calls is it that aren't working for you? The ones that are part of the story where you make choices to help the callers, or the ones that you call yourself on the phone where you press the buttons?
I also need to know stuff like which version are you playing, Windows, Mac, or Linux? And then normal version or potato version?
I'll also need to know what point in the game you're at and what you did in the game immediately before you reached a point where the call didn't work.
Even if I have all that info, I still might not be able to find out why it's not working for you without sending a dev build copy and getting your computer's error logs to look at >.<
Bugs are a lot easier to fix if I can replicate them on my end, but because I've never had problems with the calls myself, I have no way of potentially replicating the problem without knowing the exact steps you took while playing, which makes it super hard to get to the bottom of :(
Thanks for checking out the game, by the way! :3