Playing songs not available in the spotify library

[gte921n]

I am very close to dumping itunes and moving exclusively to Spotify.  I have one issue preventing it and can't seem to find a solution.

I have a few songs that friends and I have created in itunes that obviously aren't available natively in spotify - not just grayed out, but don't exist.  I thought for sure that Spotify had a mechanism for me to add in and play these songs, which are on my iphone and available through itunes.  I've played around with offline files, but there doesn't seem to be a way to "import" local songs into spotify on ios if they aren't available on spotify.  I really hope that I am missing something.  Does anyone know a way to do this?

Any help is very appreciated.  I can't wait to free up dozens of gigs, but don't want to sacrifice my playlists to do so.

[Peter__]

You need to add them as local files to the desktop Spotify then sync them over to your mobile Spotify from there.

[CanonEx]

But how can I do this?