There is a sponsor of some sort that pays for the subscription. As mentioned previously, FreeBizMag is one of the majors. In FBM's case, the primary sponsors are Fandango & Veterans Advantage. Another company, Mercury Mags is made up of people that used to work at FreeBizMags that decided to start their own. The catch with these types of companies is they get a kickback from trade mags for every trade mag sub the get you to take in addition to the free enticement.... They will make you go through a questionaire and say no to a bunch of different things before you actually get signed up for the mag you want. In some cases, they offer more good free stuff in the questionaire.
Some offers are just the company giving you a free sub to get you to try the mag, hoping you will love it & will pay for it once your sub ends. I have also gotten mags from the credit card company where they give you points that convert to subs or will give 3 free subs per year where you must cancel or they will charge your card when the sub is up for renewal. They are supposed to let you know before they charge so you can cancel. Some do, some don't - but you can call & get the charge erased if they do charge on items like that.
You'd be amazed at what you can get for free....... I currently get:
Golf, Golf Digest, Travel & Leisure Golf, Old House Journal, Redbook, Workbench, Wood, Readers Digest, Diet & Nutrition, Tennis, PC World, PC Mag, Computer Shopper, Log Home Design, Golfweek, Sporting News, Woodcraft among others that I can't currently remember.......
Entertainment mags like Interview, Spin, Giant & Blender are also easy to come by. I used to get those & found them not to even be worth free to me so I quit signing up for them.....my mailman was getting a hernia on mag day anyway..
Keep your eyes open on the message boards & you'll find many different offers. Once you sign up for FBM, you'll get emails for many offers directly as well.
HTH!