Activating World of Warcraft?

I recently downloaded the 10 day trial of World of Warcraft from their site. And in a minute i want the game but can i like buy a code or something to fully initiate it. Oh and another thing i was wondering be the prepaid cards for the monthly fee. Can you buy them at Walmart or Gamestop if not next please tell me where you can buy them.
Please lend a hand.

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dont play that gay *** game you will get addicted and wont move the house and die a lonely person trust me just dont!! yes i believe they get them at gamestop.. and best buy.. and yes you need a code.. but if i were you psyche buy a battlechest since it got a cd key for typical wow and burning crusade.. for just liek 39.99,, vs normal 19$ and burning 29$ if you buy em separate . appropriate luck