Double twist basically allows for itunes music to sync to your SD card, but thy also have double twist airsync which is over the air instead of storing songs in your SD card. I personally use mspot only bad thing is if your in an area with no data then you can't use it being it needs data.
Tapatalk'd on Evo
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Phone: HTC White EVO ROoted
ROMS: OMJ or Fresh roms prefered
KERNEL: Stock unreleased OTA
Sprint 4g speed: