I had no idea it wasn't US yet - I'm surprised as it must be such a huge market for them. Maybe their servers aren't ready for it yet, or they're having problems getting artist/label permissions.
It's also worth noting that the mobile versions of their client all rely on you having a subscription (£10 a month I think) as opposed to the situation on the destop where you can listen for free but with occasional ads.
There's also an unofficial client written a while ago on XDA (still requires a spotify subscription)
http://forum.xda-developers.com/showthread.php?t=580208
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