Your voice agent works on localhost. Here is what breaks when it meets a real phone line.

Disclosure up front: I work on Packet Exchange, a telecom API. This post is mostly the stuff we see go wrong, whoever you build with.

Getting a voice agent to talk in a browser takes an afternoon. Getting it to answer a real phone number takes a week, and almost none of that week is AI.

1. Latency you never saw in the demo

In the browser your audio goes straight to your model. On a phone line it goes caller, carrier, your telecom provider, your server, the model, and back. Measure the full round trip from a real handset, not from your laptop. If the agent waits too long before speaking, callers talk over it and the conversation falls apart.

2. Barge-in

People interrupt. Your agent needs to stop speaking the moment the caller does, or it sounds like a recording. Test this on a real call with someone who interrupts on purpose.

3. Numbers are not just numbers

The number your agent calls from decides whether the call is answered. Local numbers get picked up more than unknown ones. Numbers that make lots of short calls get labelled as spam by the carriers. Plan which numbers you use before you scale, not after.

4. Silence and dead air

Phone lines have silence detection, voicemail and hold music. Your agent has to know the difference between a person thinking and a voicemail greeting, or it will happily pitch an answering machine for two minutes.

5. Logs you can actually read

When a call goes wrong you need the call record and the transcript side by side. Set that up on day one.

Where Packet Exchange fits

We give you the phone side in one place: numbers, voice calls, SMS and AI voice agents behind one API key, so the agent and the line are not two separate projects. If you want to try it, there is a free account here: https://packetexchange.io/register?utm_source=devto&utm_medium=article&utm_campaign=voice_agent_phone_line

What broke first when you moved your agent onto a real number?