On: Build a Twilio Hard Phone with SIP from Twilio, Raspberry Pi, and Asterisk

[superuser2]

Voicemail, 7-digit dial (most SIP providers only take 10), forwarding, filtering, etc.

Twilio could theoretically handle these things for you, but they're typically handled in a PBX.

[swalberg → superuser2]

Hm, maybe I should have been more specific. Given that this is an interesting hack to get a PSTN call to an analogue set through Twilio, why did they bother with the SIP proxy?

[superuser2 → swalberg]

I'm not sure I understand your question, but I think it's because the ATA (like most modern/cheap ATAs) only speaks SIP.