Might as well post a bit of info about this. I've now used one and it's pretty impressive.
I'm not too convinced about the phone side of things. The Serene was an absolute joy to use as a phone, it seemed so well thought out and simple/clean. Everything just worked.
The Serenata doesn't seem as simple when it comes to just ringing someone as the Serene. The loss of any form of numpad makes it a bit of a nightmare dialing in numbers, and even more of a nightmare texting. No camera either which is bit of a bummer.
The MP3 player side of though, is really really incredible. I'm not sure what I'd compare it to sonically, but the internal speakers are definitely better than any MacBook Pro speakers I've heard (which are pretty impressive considering their size). The Serenata's built in speakers really are, absolutely stunning for their size/a phone. When it comes to plugging in headphones, it's pretty impressive too. The sound quality is like no other MP3 player I've heard, really very very impressive.
It also feels pretty solid and is the perfect shape to fit in your hand, and sits at the bottom of your pocket fantastically (others don't I've found). I can't say I found the wheel above the screen an issue, I kinda prefer it that way, feels more natural.
Not sure about the price though
