Why don't you just randomly calling real businesses and stores and just start talking with them? Ask them random questions. I figure if you make enough of these calls on a regular basis, you will desensitize yourself to the act of calling. The first few days of calling will be the worst, but your body should get used to it and your reaction to phone calls should start to diminish the more real phone calls you make. Probably would work better than a "fake phone call app" since with the fake app, you already know it is fake, so the high stakes aren't there.