[mraison]

> Limit the amount Twilio can charge us

This is unfortunately easier said than done. You'd expect Twilio to let you set a max spending limit in your account settings. Instead this is what they tell you to do: https://support.twilio.com/hc/en-us/articles/223132387-Prote... (notice the PHP snippet too)

Essentially, setting up a webhook to receive alerts from Twilio, and then calling a Twilio API to suspend the account. Your webhook better be up and running flawlessly if you don't want to go bankrupt. Why can't they do it themselves?