Alright, so let me begin by explaining that this is a bit scandalous, but quite a bonus for hungry students. Everytime you go to Wendy's you get a reciept that advertises the ability to get a free single hamburger burger (the big one, no JR. crap) by taking the phone survey. The survey takes about 5 minutes, is relatively easy, and at the end you get your validation code. For almost every single day last week, to see if this would work, I used the reciept I got from the previous day's burger to score another burger. I took the surveys as I was eating, and bam - free lunch again tomorrow.
If you really want to get into technicalities, it does say "only one free per 30 days", but considering they take no personal information from you, there really is no way to confirm this (ignoring the free burger on the reciept from the day before, lol). Regardless, use those free burger reciepts!