mobile clients have their own set of bandwidth issues. I play 1 playlist on my phone, it is available locally (all downloaded long ago), and yet spotify has used over 2gb of bandwidth in the last 20 days. There's a huge thread about it on the spotify forums somewhere.
If your phone is low on space to cache your entire Spotify offline library, it will continuously stream/thash for cache space as you play it all.
No, I'm pretty sure they don't.
That's a good question, maybe on WiFi? It certainly shouldn't when on 3G/4G.
No, per the "spotify technology" article linked to in the discussion-.