Twilio client only with HTTPS
From the beginning of december 2015 Twilio will only work via HTTPS.
You will need to replace the integration code of your call buttons with new integration code, which explicitly adds 'https' before url of 'track.js' file. (old integration code uses so called 'protocol relative url' starting with two forward slashes '//')
URLs for Twilio numbers / Twiml apps in Twilio account can remain with http if there is a redirect or if you have also http enabled.
Twilio only a...