1) Once you see it it in the iTunes FIle Sharing-GarageBand-Documents section, drag the Rignton file (.m4r) to the desktop
2) Drag the .m4r file onto the iTunes Library. iTunes detects it as a Rington and puts it into the Tones section of the Library
3) When syncing your iPhone, select that Rington in the Tones section
Hope that helps
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