CosVoice is a finished phone line for the assistant you already use. xAI's Voice Agent Builder is a console for building voice agents from scratch. Both put a number in front of an AI; only one of them arrives working.
Written 18 September 2026, the day we went through their console and docs line by line. Everything below was true that day. They ship fast, so if a row is out of date, tell us and we will fix it.
| CosVoice A finished line for the assistant you have | xAI Voice Agent Builder A console for building voice agents | |
|---|---|---|
| A real phone number for the AI | Yesyour area code, plus its own email | Yesone free number, or bring yours over SIP |
| Works with the assistant you already have | YesGrok Bot, Claude, ChatGPT, Cursor | Noyou build a new agent in the console |
| Connected by pasting one address | Yespaste cosvoice.com/mcp into your assistant, press Allow | Partlytheir MCP support adds tools to an agent you built first |
| Ready without building anything | Yesanswer a few questions and it is live | Partlya basic agent takes a couple of minutes to assemble |
| Wakes your own Bot when a call ends, a text arrives, or mail lands | Yes | Nothe console notifies your team |
| The line has its own email address, in and out | Yesyou@cosvoice.com | Partlyit can send through your email account |
| It calls people for you | Yesrestaurants, offices, errands, from a plain-English brief | Partlyyou build the agent and write the brief |
| Answers the calls you miss on your own mobile | Yesforwarding set up for you, answered as your assistant | Partlyyou can point your forwarding at it |
| The summary comes to you | Yesyour inbox and your Bot's chat, every call | Partlyrecorded and transcribed in their console; sending it on is your job |
| Keeps the written call, not the audio | Yestranscripts and notes only | Noevery call is recorded |
| Texts from your own mobile count as instructions | Yes | No |
| A morning brief, and nothing on a quiet day | Yes | No |
| A call outcome you can send as a link | Yes | No |
| Everyday app actions, after you confirm | YesInstacart, Uber Eats, calendar, ready to use | Partlywork tools you connect and wire into each agent |
| Gets things done where there is no app to connect | Yesit phones the shop, the vet, the landlord | Partlybuild an outbound agent for it |
| Front desk mode: your hours and rates, written up after each call | Yesbrief it once, in plain words | Partlybuild it with their knowledge base |
| Never reads a card number back | Yesa rule of the product | Partlya guardrail you switch on |
| Says it is an assistant when asked | Yesa rule of the product | Partlya guardrail you write |
| Hands the call to a person | Yesholds, then rings your mobile | Yestransfer to a human |
| Choose the voice | Yes38 voices in two sets | Yes80+ voices, and cloning your own |
| Build your own voice product on it | Noone line, one assistant | Yesmany agents, your own tools and models |
CosVoice is the phone, the email, and the nudge that wakes the assistant you already talk to. The other way round, you build a second assistant and keep it in step with the first.
A table booked. A quote captured with the number. A note waiting in your chat, whether or not you were there to hear the call.
No console, no tool wiring, no prompt to maintain. Answer a few questions, pick a number, and the line works on the first call.
We keep the written call and the transcript, never the audio, and what your line hears is sealed to your line.
If you are building a voice product of your own, xAI's builder is the better tool, and it is good: a free number, 80-plus voices, voice cloning, a knowledge base, and your own tools wired in. CosVoice is the other job. You already have a Chief of Staff, and you want it answering a real number today, with the calls written up and waiting for you. Facts here come from xAI's own console and docs, checked 18 September 2026. If something has changed, tell us and we will fix it. See also the wider comparison.
A number in your area code, connected to your Bot in one paste. About a minute.
Yes. Any assistant that supports MCP connects with one paste: Grok Bot, Claude, ChatGPT, Cursor, and others. Any of them can be woken by CosVoice if it has a webhook URL and a token. Developers also get a REST API and signed webhooks.
No. The line works on its own. Call it, text it, and ask it to make calls from your dashboard. If you do have a Grok Bot, or another assistant that supports MCP, connecting it lets your assistant make calls and read the summaries by itself.
Give your Bot the address cosvoice.com/skill and say “read this and give yourself a phone number.” That page is written for assistants: it explains the one URL to connect, how to pick a number, and how to place calls. Or paste https://cosvoice.com/mcp into your Bot's MCP settings yourself and click Allow.
On a call, no. It never gives out a card number or agrees to a charge, so a booking or appointment is the most it commits you to. Your plan's minutes are the only thing the line itself spends, and app orders (dinner, groceries) go through only after you confirm.
Pick a number, save the contact, make the first call. About a minute.