Y'know, this poster hit it right on the head...
...until someone writes a decent XM player for the Curve, a viable option is ORB and uXM.
I've been a loyal XM subscriber for many years (and used to listen all the time on my Treos); I cannot believe that XM would gouge its current subscribers for mobile access when PC access is free. In Yiddish, we call that chutzpah.
I currently use Orb and uXM and it works great.