Yes, sidetone (hearing your own voice through the handset) makes all the difference! I'm not exactly sure why, but I find it so much easier to talk on the phone when there's a sidetone. In general, for me, talking on the phone is like talking into the void, and sidetone at least gives me the assurance that, yes, it's still working. Like the little inset video feed of yourself when you're on a Skype call.

Nice work! Maybe I missed this, but have you considered simulating a dial tone?