DoubleTwist has just been updated with the long-promised and highly-anticipated wifi syncing feature, which has been dubbed "AirSync." Unlike the player itself, which is free, AirSync is an add-on that will run you $4.99 (or 99 cents for the first 10,000 users), you will see a link to purchase it when you start up the updated DoubleTwist Android player. In addition to the phone app, users will need to make sure to update their desktop client, which is available for the Mac and PC.
If you jump on the DoubleTwist wagon, make sure you visit the Android Central Forums to discuss the new update. If you haven't used the program (or any syncing app), check out our handy guide to syncing music onto your Android phone. [DoubleTwist]