Your nixamp stream now has a phone number

nixamp streams now have a phone number. Call 408-357-2326, key a six digit code, and you are listening to somebody's live stream. No app, no account, no data plan. It works on a flip phone.

I built it in an afternoon and most of that afternoon was spent learning that almost everything I assumed about phone numbers was wrong.

The part that turned out to be easy

I expected the audio to be the hard bit. It is not. A nixamp stream is an MP3 over HTTP, and Telnyx will play a URL straight into a call. One API call, playback_start, and the caller is hearing the stream. My server never touches a byte of audio.

The IVR is the same shape. Answer the call, ask for six digits, look the code up, start playback. The whole thing is a small state machine over webhooks. If the stream has finished you hear when it ended and get offered a text for next time.

The part that turned out to be expensive

I started on a toll-free number, because that is what a call-in line is supposed to have. 888-ROOM-818, which I was quite pleased with.

Then I priced it.

Toll-free inbound is $0.015 a minute. A local number is $0.0032. That is 4.7x for the same call. On a line where people stay on for hours, that difference is the entire cost of the product.

It gets worse. Telnyx sells channel billing: a flat monthly fee for unlimited inbound minutes. It is the obvious answer for a line people camp on. Toll-free numbers are structurally excluded from it. Standard DIDs only. So the number I picked for being the friendly one could never reach the cheap tier, at any volume, ever.

My next idea was to keep the toll-free as the front door and forward it to the local number. This does not work either, and the reason is worth knowing. Telnyx bills you for both legs of a forwarded call. You pay the toll-free inbound and the outbound leg, for the whole duration. Forwarding is strictly more expensive than just answering.

And you cannot transfer your way out of it. The caller's connection is the toll-free leg. A transfer bridges a new outbound leg to it; hanging up the original hangs up on the caller. There is no handoff that drops your own cost.

One more, which I only checked because I was about to write it in a footer: US toll-free numbers are generally not reachable from outside the US. 800, 888, 877, 866. The called party pays, and that billing model does not cross borders, so most foreign carriers will not route it. The number I was about to advertise as the international-friendly one is the one international callers cannot dial. A plain local number works fine for them; they just pay their own international rate, like any other call.

So the published number is a 408. The 888 still answers, for anyone who has it, as a vanity alias that costs more.

Getting told

The other half is following. You follow a broadcaster, and when they go live you hear about it: web push, email, or a text, whichever you asked for. Web push covers the browser, the installed PWA and the desktop app, because all three are the same subscription wearing different clothes. One person with a laptop, a phone and a desktop is one account and three subscriptions, and gets three notifications.

There is a subtlety in the settings switch that I got wrong first time. The web toggle is not a preference, it is a conjunction: your stored preference, and the browser's permission, and a subscription the server actually holds. A browser will only prompt for permission in response to a click, so the switch can never be turned on from a page load, however much the saved preference insists it should be. If you show only the preference you get a switch that reads on while nothing arrives.

The bug I want to tell you about

Announcing is not going live. A publisher heartbeats every ninety seconds for as long as it is up. If you notify on every announcement you notify forty times an hour. So the notification fires on the transition, and again if a stream stops and comes back, because a second run really is a second broadcast.

That one I got right. Here is the one I did not.

Somebody calls, hears "press 1 to get a text when they are live again", and presses 1. I stored that in a Map. Most of nixamp is deliberately ephemeral, and I had been enjoying that: the directory is a four minute TTL and a heartbeat, no database, a restart costs one heartbeat instead of a migration. It is a good design for a list of what is on.

It is a terrible design for a promise. Every deploy silently dropped everyone who had pressed 1. The text never came. Nothing logged an error, because nothing had failed. A promise made to a person on a telephone and then quietly forgotten is worse than never having offered it.

The fix is a mirror rather than a replacement. The in-memory maps stay exactly as they were, so every caller is still synchronous and every existing test still describes the same object. Writes get echoed to Postgres and read back once at boot. Only the two things that were always meant to outlive the stream: the reminders, and the record of what ended and when.

Taking a reminder is DELETE ... RETURNING rather than a select and then a delete, so two streams going live at once cannot both read the same list and text everybody twice. And that take is what clears it, which is exactly why a number left behind by a process that has since been replaced still gets its text from whichever process succeeded it.

I tested it by causing the bug on purpose:

remembered 1 stream(s) that had ended.
1 caller(s) are still owed a text.
texted 1 of 1 waiting on 754984.

That is a server that restarted between the promise and the delivery. It never heard the phone call. It read the promise out of Postgres at boot and kept it.

What I would tell past me

Price the phone number before you fall in love with it. Check whether the cheap billing tier even applies to the kind of number you bought, because the answer can be a flat no that no amount of volume will move.

And be careful which things you let be ephemeral. Ephemeral is a good default and I would keep it for almost all of this. But the moment you say the words "we will tell you later", you have written a durability requirement, and a Map is not going to honour it.

nixamp is at nixamp.com. The phone number is 408-357-2326.