If for some pressing genuine reason you can't, then I bet the controllers will do their damnedest to help you out.
That is often me ... and I should add, I have nothing but praise for the ATC guys I have dealt with and I usually get given direct clearances through Willy, once over the top of fighters doing circuits.
AOTW, not all of us are mobile phone savvy or even own a phone that can do that stuff. Access to a computer while traveling is not always that easy either