I've only had TU respond by mail no matter how the contact was initiated. That said, I as a rule don't do fax. Dave thread from earlier today, on why faxing disputes is a problem: http://consumers.creditnet.com/straighttalk/board/showthread.php?s=&pgnum=1&postid=241849#post241849 Sassy
Don't forget they have 5 days from the end of the 30 day dispute period to notify you. You will most likely get a report in the mail in the next day or 2.
I've never heard of TransUnion (fka Trans Union) listing a fax number as part of their dispute procedure. What's the number, and how did you get it?
The fax # that I used is (714) 447-6032 and I got it from the FAQ here. The very first fax that I did was on 8/21/02 and I got a letter and an updated CR from TU on 9/02/02 dated 8/29/02. (It worked for me and a co-worker of mine)