Can you imagine how annoying ads in the voice interface would look like? Ugh
You'd most probably wouldn't be able to tell for sure. Ads will be subtle and flow as background music to the onversation. Talking to the AI while on your daily commute will make you thirsty for some sort of hot beverage while ChatGPT tells you all about sirens in Greek mythology.
In general, any textual embedding in the ad or system prompt would result in an abjectly terrible user experience. I must assume it will just be banner ads etc