Not only can you download Vita games early, you can buy boxed copies of first-party titles early as well. GameStop currently has copies of Little Deviants,Uncharted, Hot Shots, Wipeout 2048, and ModNation Racers in stock online right now. They ship within 24 hours, the site notes, or you can use the site to check for stock at your local store.
The Vita hardware will officially be available February 15 in the First Edition bundle, but it's possible you already have a Japanese unit, in which case youshould be able to play these cartridges.