If I call tech support or the bank or whatever, I don't want, need nor expect to see the other person's face. In general, video calling isn't widely used except in multi-person meetings, or when calling a loved one overseas. The avatar is not needed.
Also, give your AI agent a phone number where I can reach it, or give it its dedicated app or whatever, but default to "handset mode" like a regular phone call. Let me put it on speaker if and when I want to. Turning the interaction into a regular phone call will go a long way towards making the conversation feel more natural. Interacting with Siri and Alexa feels unnatural; adding an animated avatar to a disembodied voice won't help, even if the conversation itself flows naturally. I know, a phone call isn't suitable for every interaction, especially when collaborating or co-creating with someone, but it covers most cases.
But I guess a simple audio call is harder to monetize.