The math the pricing pages don't show
Take a five-person contractor. On RingCentral's published August 2026 pricing, five seats run $100 to $175 a month billed annually ($150 to $225 monthly), before the AI Receptionist add-on from $39/mo, booster packs, taxes, and fees. Every hire adds a seat.
Now price the raw ingredients at published carrier-API rates (Twilio's public list prices, as one well-known example): a local number is about $1.15 a month, inbound voice about $0.0085 a minute, SMS about $0.0079 a message, and other wholesale carriers publish rates as much as half of those. That same business doing 2,000 call minutes and a few hundred texts consumes roughly $20 to $30 of underlying telecom a month, for the whole team, not per person.
The gap between those numbers is what you pay per-seat platforms for: the portal, the apps, the packaging. It is a fair trade for some teams. But it means the interesting question is not "which per-seat platform", it is "who assembles the cheap ingredients into my phone system, and what do they charge for that."
What a phone system is actually made of
A phone number
Local or toll-free. At wholesale carrier rates a local US number is about $1.15 a month.
Carrier connectivity
The part that actually moves calls. Wholesale usage pricing runs on the order of a penny a minute, inbound local voice is around $0.0085/min at published carrier-API rates.
Routing rules
Business hours, menus, ring groups, failover, voicemail. This is software: on a per-seat platform it is the admin portal, in a DIY build it is code you write and host.
An AI receptionist
The piece that answers when humans cannot: questions, bookings, messages, 24/7. Per-seat platforms sell this as an add-on (RingCentral's starts at $39/mo). In a custom build it is wired into the flow wherever you want it.
Texting
Confirmations, missed-call text back, follow-ups. Wholesale SMS is about $0.0079 per message plus carrier registration surcharges, but US business texting requires A2P 10DLC registration either way.
The three ways to build it
1. Full DIY on carrier APIs
Rent numbers and usage directly from a carrier-API provider, write the routing logic yourself, host it, and wire in an AI voice agent. This is the cheapest raw cost and the most customizable option in existence, your call flow is literally code, so anything is possible.
The honest catch: you are now a telecom engineer. A2P 10DLC registration before you can text, E911 addresses, webhook servers that must never die, and nobody to call when it breaks. Right for businesses with a developer on staff who wants the project. Wrong for everyone else.
2. Self-serve per-seat VoIP
RingCentral, Nextiva, Ooma, Grasshopper: sign up, configure the portal yourself, pay per user per month. Zero engineering, fast setup, and the right answer when your team also lives in the platform's meetings and messaging. The costs are the per-seat math and the tier-gating, we compare them honestly in our alternatives guides, and your call flow is limited to whatever the portal supports.
3. Done-for-you hosted (the middle path)
The DIY architecture, custom routing on wholesale-priced infrastructure with an AI receptionist wired in, but a team builds, hosts, and maintains it for you, priced flat per business instead of per seat. You get DIY-grade customization without becoming the engineer, and the bill stays the same when you hire.
This is what we do at Everyday Software, so weigh our bias accordingly. It is also, for most businesses under about twenty people whose phones mostly ring inbound, the only path where "exactly my call flow" and "nobody here manages a phone system" are both true. Details on the hosted phone system page.
Let AI design it: describe your call flow in plain English
Whichever path you pick, the first artifact you need is a call flow: what happens, step by step, when someone calls. This used to mean a whiteboard and a consultant. Now you can type it.
Our free call flow builder takes a plain-English description, "ring the office during business hours, AI picks up after 20 seconds and books appointments, after hours the AI handles everything, text anyone we miss", and AI maps it into a visual flow you can rearrange block by block. No email gate. Hand the result to your developer, use it to pressure-test a per-seat portal's capabilities, or send it to us and we will build it as designed.
Build Your Own Phone System: FAQ
Pricing facts reflect published rates as of August 2026 and may change: RingCentral RingEX $20-$35/user/mo billed annually ($30-$45 monthly), AI Receptionist add-on from $39/mo; Twilio published list rates of ~$1.15/mo per US local number, ~$0.0085/min inbound local voice, and ~$0.0079/SMS segment before A2P carrier surcharges.
Skip the build. Keep the custom.
Describe your call flow, we build and host it, AI receptionist included, one flat monthly price.