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I'm using the Droid RAZR just fine with Spotify - my phone appears as the "XT910" under "Devices" in the official app.
If you're having problems, it could be a dodgy firewall blocking connection. My PC is wired and phone is wireless, but it also works on my Netbook which is wireless.
Make sure your wireless option is turned on on the phone and that they're both connected to the same network/router!