Note: This document applies to Mac OS X 10.3 through 10.3.9.
Just put a comma (",") between each recipient's name or phone number in the fax's To: field, like you'd do to send an email to several people.
If the fax isn't supposed to go to multiple recipients, make sure there are no commas in the To: field. This includes contacts whose name contains a comma (such as ", Inc.").
Using a comma to pause dialing
If you need to fax to a number but also need to use commas to pause when dialing that number (you're using a calling card, for example), check out this tip: Put the first part of the phone number, including commas to pause dialing where needed, in the Dialing Prefix field. Put the rest of the phone number in the To field.
If you want to fax to more than one number that requires pausing with a comma, either send the faxes separately or create an Address Book contact entry for each number (with commas in the Address Book entry) then fax to both Address Book contacts, separating them by a comma. If you're using a "temporary" calling card number, sending separate faxes might be easiest.
Related documents
152362: Mac OS X 10.3 Help: Using special characters in the phone numbers your modem dials
25670: Mac OS X 10.3: Faxing - Application Unexpectedly Quits When Sending to Many People