You can setup web 2 fax for anonymous users easily without any coding. You just need to set permission "can use ictfax" to anonymous user. From admin -> People -> Permission -> can use ictfax. Click the check box against anonymous user.
For enabling email to fax for anonymous users, you might have to change source code. Because whenever someone sends an email at the ictfax server e.g. (email@example.com) then the senders email is verified from the list of authenticated (registered) users. So you might need to remove that check. You can see related code in Feeds module (plugins -> FeedsFaxProcessor.inc).
I hope that helps.