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A fax number looks exactly like a regular phone number because it is one: the same ten digits, the same area codes, dialed the same way. The difference is what answers. A voice number reaches a person or voicemail; a fax number reaches a fax machine or an online fax service that expects the screeching handshake tones of a fax transmission, not a conversation.
| Phone number | Fax number | |
|---|---|---|
| Format | Ten digits with an area code | Ten digits with an area code, identical format |
| What answers | A person, voicemail, or menu | A fax machine or online fax service |
| What it accepts | Voice calls, often texts | Fax transmissions only |
| Wrong use | Calling a fax number gets you modem screeching | Faxing a voice number reaches a confused person |
You hear the fax handshake: a series of beeps and the high-pitched screech that is the two machines negotiating the connection. That sound is data, not a malfunction. The receiving machine is waiting for your machine to start sending page images, and since your phone cannot do that, the call just sits there screeching until one side hangs up. If you ever need to check whether a number is a fax line before sending, calling it and listening is the fastest test: screeching means fax, a human voice means you have the wrong number.
Sometimes, with a catch. Old combination machines could share a line and switch modes based on what called, but the behavior was flaky: an incoming voice call during a fax could interrupt the transmission. Modern offices usually keep them separate because the failure mode is a lost fax. Some online fax services let a single virtual number receive both, routing voice calls to voicemail and fax tones to the fax inbox, but a physical fax machine on a shared line remains a compromise.
Most new fax numbers are virtual: an online fax provider assigns you a number from the regular numbering pool, and incoming faxes arrive as email attachments or app notifications instead of paper. There is no physical machine involved, which is why a small business can have a fax number without owning a fax machine. The number still behaves like a phone number to the outside world, so anyone with a fax machine, or another online service, can send to it.
Start with the obvious: the contact page, the footer of their emails, or the intake paperwork they sent you. Medical offices, law firms, and government agencies still print fax numbers on almost everything. If it is not published, call their main voice line and ask: fax numbers change less often than staff, so the receptionist usually has it. Do not guess by tweaking a voice number by one digit; faxing a stranger's line is how documents end up on the wrong desk.
No. LetterAgent sends faxes to US and Canadian fax numbers; it does not receive them, so there is no inbound fax number to give you. You describe the fax to your AI assistant, approve the exact quoted total with the page count verified, pay once through Stripe, and the fax is sent. The service is currently in testing, so describe faxing as available in testing and confirm current status with your assistant before relying on it for anything time-sensitive.
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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