Ask ten people what makes an AI phone call feel robotic and most won't mention interruption handling by name, but it's very often the actual cause. An agent that talks over you, or one that stops dead the moment you cough, both feel wrong in a way that's hard to articulate but easy to notice.
The naive approach, and why it fails
The obvious way to handle interruptions is to just stop the agent's audio the instant any sound is detected from the caller's side. This sounds reasonable and behaves badly in practice, because it means a caller saying "mm-hmm" or clearing their throat cuts the agent off mid-sentence. Do that a few times in one call and the agent feels twitchy and unreliable, stopping and restarting for no clear reason.
The opposite approach, ignoring the caller entirely until the agent finishes its planned sentence, is worse. A caller who's genuinely trying to interrupt with an objection or a correction gets talked over, which is one of the more frustrating things a phone system can do to someone.
What actually has to happen
The real answer sits between those two extremes, and it requires the system to distinguish a genuine interruption from background noise or a short acknowledgment. That distinction runs on how much the caller's voice overlaps with the agent's own recent output, and for how long. A brief overlap that fades is treated as an acknowledgment. Sustained overlap, held for a few hundred milliseconds, gets treated as a real interruption and the agent yields.
There's a second layer to this that's less obvious: echo. If the agent's own voice is playing back through the phone line and getting picked up by whatever's on the caller's end, a naive system can end up interrupting itself, hearing its own audio as if the caller were talking. Getting this right means treating the agent's recent output as a reference signal and filtering it out of what counts as "the caller talking," rather than just listening for any sound at all.
Why this is worth the engineering effort
None of this shows up as a line item anyone can screenshot from a features page. It's not a visible UI element. It's a behavior that's either right or noticeably wrong the moment a real conversation happens, and it's one of the clearest signals of how much actual engineering has gone into a platform versus how much is a thin layer over a generic model with no real-time tuning underneath.
How to test it yourself
Call a number running the agent you're evaluating, and interrupt it on purpose, mid-sentence, with a real objection: "no wait, that's not right." Then separately, just say "yeah" or "okay" while it's talking, without meaning to interrupt. A well-built system stops for the first and keeps going through the second. That's the entire test, and it takes about thirty seconds to run, but it tells you more than most of what's on a comparison page.