I felt stupid when I found out by myself that DUN had to be Dial Up Networking..
Well, I tried to do what you said, putting the fax number in a normal DUN connection, and tried to call with "Bluetooth Fax Modem" and "Bluetooth modem", but none of the connections made the phone show "F" instead of a "F"...
How can the phone know when to use the "F" ?
Thanks again!