Mostly it's Twilio costs. I spend an unconscionable amount on my cell phone bill due to e.g. international roaming or international phone calls for sales/support, but that doesn't even crater the approach to the bridge of what Twilio costs me. (And I rush to say "I'm totally fine with that, and wish I spent 100X as much, because to a first approximation that would imply revenues 100X higher than they are currently.")

re: cell phone bills, have you thought about getting a raspberry-pi or a larger server running asterisk with chan_dongle, and using a prepaid sim card at each country as your "gsm gateway"(1)?

(1) http://blog.carrier-connect.com/raspberry-gsm-gateway/

Don't forget one of Patio11's products is almost entirely leveraging telecom services for it's functionality: https://www.appointmentreminder.org/

So I doubt he is just talking about a generic office phone when mentioning teleco services.