Bobby Kotick, CEO of Activision Blizzard, noted during today's quarterly earnings conference call that the publisher may begin charging for user-generated songs uploaded through Guitar Hero World Tour 's GH Tunes service. Kotick has previously stated that GH Tunes has the "potential" to be one of the "credible alternatives to iTunes." Kotick boasted that the latest Guitar Hero has, since launch, seen some 25,000 user created songs uploaded to GH Tunes. The company expects to see "up to 100,000 by year end." "The ability to offer these songs on a subscription basis may very well result in the newest subscription opportunity in our portfolio," Kotick said, hoping to add to the subscription revenues the recently merged publisher enjoys from World of Warcraft . The MMO is largely responsible for $271 million in revenue for the previous quarter alone.