I just tried to import a number of VCards and it worked great except for Work Fax numbers, the cards I'm importing use the following format:
TEL;WORK;VOICE:1 (999) 555-0100
[B][COLOR=#FF0000]TEL;WORK;FAX:1 (999) 555-0102[/COLOR][/B]
ADR;WORK:;;1234 Somewhere Lane;Sometown;Province;P0STCOD;Country
LABEL;WORK;ENCODING=QUOTED-PRINTABLE:1234 Somewhere Lane=0D=0ASometown, Province POSTCOD=0D=0ACountry
Everything comes in correctly except the TEL;WORK;FAX is changed to a simple Work phone number.
I got around it by adding a line to the cleanup function in rcube_vcard.php that replaces TEL;WORK;FAX with TEL;BUSINESSFAX (not being a regexp guru I just did a simple replace)