I had a very god fax solution with previos LibreOffice version using spadmin and brpcfax script for a Brother MFC device. After upgrading to 4.3, I installed fax4CUPS 1.29 as recommended. However, if I print to one of these fax devices (e.g. efax), LibreOffice spools a print job immediately without asking for a fax number - probably they are not recognized as fax devices ...
You need to set DialMethod=Option as default in CUPS printer settings - then LibreOffice displays a dialog box for entering a fax number. For using the Brother MFC fax option, you need to patch the .ppd-File (usr/share/cups/model/brfax_cups.ppd) and add these lines: *OpenUI *Dial/Dial Method: PickOne *OrderDependency: 30 AnySetup *Dial *DefaultDial: JobName *Dial JobName/Job Name: "" *Dial Manually/Manually: "" *Dial Option/Option: "" *CloseUI: *Dial Furthermore, you need to patch the CUPS filter for Brother Fax (/usr/lib/cups/filter/brfaxfilter) - after this line num="`echo $5 | tr ' ' '\n' | grep -i "$FAXNUMLABEL" | sed s/"$FAXNUMLABEL"//g`" add ## DialMethod=Option supplies fax number in $3 if [ "$num" = "" ];then num=`echo "$3" | tr -d '/ -' | egrep '^[0-9]{3,16}$'` fi