Seen alllll kinds of zoom attachment lens paraphernalia....popping up everywhere...esp at fleabay.....got a couple of universal models from ebay to try them out...
interesting cheap knock offs....work ok...but..they don't quite do even digital camera quality.

this one here for the sony....looks real good....but....I'm not too sure of the quality that would be garnered compared to a proper camera ...a camera which was actually designed and built to take pictures...not a phone that is attempting to do it all.
at least this early in the devel of such toys...
I'm sure some phones would work better than others...and some attachments would work better too ....hm.
Give it a few years...if the zoom lens is just a shiny fad-toy it'll disappear. If they get realllll good and the interest is there for total camera replacement...then it'll stick around as a must have accessory and the quality will only improve.