Well that sux! Some of us are a little behind the times and do not have wifi because our cable connection performs almost the same job as a wifi connection would. Here I was a Splendour on the weekend trumpeting Spotify and saying it was pretty darn good. Glad I only picked up the 30 day free trial. Why only WiFi ... what is the reasoning behind this?
I go to a school that literally does not have or allow wifi because of security restrictions. thank you US government. Because of this my phone just downloaded over half a gig of music when i made a playlist "listen to offline". There needs to be a wifi-less method of syncig the iPhone to your computer when there is a USB connection. Since that used to be the only way to sync your device I don't understand how that can be that difficult, and why I just paid $10 because spotify destroyed my data usage.
As long as your laptop/desktop has wireless, you should be able to synch to your mobile device by creating an ad-hoc wireless network on your PC and connecting your mobile to that. This post explains how to do this in Windows 7.