I went through a zombie exam, got "H M M, this sucks, form submission failed. hangs up" Error recovery is a bit, ahem, challenging in a call flow, but you might try to make things a wee bit more graceful. Still, I understand it isn't meant to be immediately productized.

As a product, by the way, this has clear commercial potential. Can I mention again how much Twilio is going to disrupt whole industries?