Looking for option for 3-way file sync
I use SMEStorage. I actually use 2 Storage Clouds on it. My home WebDav Server and SkyDrive.

My files physically reside on my home WebDAV server and on SkyDrive. I have a phone to SkyDrive folder sync setup through the SMEStorage App for some docs/files.

SMEStorage has the ability to encrypt files uploaded to it and then decrypt on the fly from the  Client, which suits me. It uses AES-256 and does not store the private key so if you lose the key your stuffed but again this approach suits me.