OK so you saw the title and are wondering "free wow? must be hax." well no its actually fairly simple.
Step 1) You need a pay pal account. The catch? no catch, it can have fake info(except email for activation, but you can make free email accounts anywhere) and DOESN'T need ANY money in it.
Step 2) Use your pay pal account to add game time on the WoW website.
While Blizzard is charging the PayPal account, you can log on. about a 5 minute window or so. After that processing time, you will receive an email from PayPal about not being able to pay etc....but you are already logged on!
Process must be repeated if you log off. Enjoi!
**Disclaimer: I have currently had no problems with this but it is possible that your account can receive a ban (whether it be 24 hours or permanent) if Blizzard smartens up and notices your playing without paying.**