Have a customer that found Twilio on line and wanted to port their telephone numbers.
Thought I would test the service first and make sure it all worked as expected.
Outbound calling setup was pretty straight forward, no issues. Could not get incoming to work at all.
After about 6 hours of debug and working with Twilio support via email, it appears that the INVITE size being sent by Twilio is 1567. Our DrayTek router has a max MTU of 1500, 1496 with hardware acceleration.
Just wanted to give a heads up if others are having the same issue.