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Your business phone app is built for voice calls and texting, not faxing, and most providers treat fax as a separate feature they never built. OpenPhone and Quo state outright that fax is not supported. The practical fix: pair your phone app with an online fax service and give callers a dedicated fax number.
Voice and fax ride the same phone line in the old world, but inside a modern phone app they are completely different products. A business phone app is engineered around low-latency voice, SMS/MMS, voicemail transcription, and call routing. Fax needs a different stack: document rendering, page-by-page transmission with retries, busy-signal handling, and confirmation pages. Building it means maintaining a second product with its own support load, its own compliance exposure (junk-fax liability), and demand from only a slice of customers. Most providers did the math and skipped it.
There is also a technical wrinkle. Fax over an app's voice channel is unreliable because voice codecs compress audio in ways that corrupt fax tones; reliable internet faxing needs a dedicated fax protocol on the back end. So even a provider that wanted to bolt fax onto voice calls would have to build separate infrastructure, not just add a button.
| Service | Fax support | What to do instead |
|---|---|---|
| OpenPhone | Not supported, per its support FAQ | Use a separate online fax number |
| Quo | Not supported | Use a separate online fax number |
| Google Voice | No fax feature | Use a separate online fax number |
| Most VoIP business apps | Voice and SMS only by default | Check the pricing page: fax is usually a separate add-on or absent |
The pattern holds across the category: if a phone app's pricing page does not mention fax explicitly, assume it is not there. A few unified-communications platforms do bundle fax, but they sell it as a distinct feature with its own number, which tells you how separate the two really are.
Get a dedicated fax number from an online fax service and publish it separately from your voice number. This is how most small businesses actually operate: the phone app handles calls and texts, and the fax service handles inbound and outbound faxes, each on its own number. Two practical tips: put the fax number on your website and email signature exactly where clients look for it, and set the fax service to email you a PDF of every incoming fax so nothing sits unseen in a portal.
LetterAgent's fax service is available in testing for US and Canadian fax numbers: you describe the fax to your AI assistant, approve the exact quoted total, and pay once per fax. Like other online fax options, it is separate from your phone app, which is precisely the point.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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