Sony is aiming to get more developers on its PlayStation Mobile platform, and as such has announced that it is waiving the $99 license fee. That means developers will be able to create a game for the PlayStation Mobile platforms, including the Vita, essentially for free.
The PlayStation Blog announced the move, and was frank about its intentions of getting more development on the platform. Earlier this year Sony started promoting a weekly free game for PlayStation Mobile, aiming to drive more players--which presumably, would then drive more developer interest as well.
You can register at the developer portal. The blog did mention this as an effort for this summer, which could mean the fee will return eventually.