iPhone connection/buffering issues

[platypus]

I have an iPhone 4, and a 3G connection. When I am listening, it sometimes will stop playing in the middle of a song, or won't be able to play the next song. But I don't have any problem if I turn off the wi-fi on my phone. Is there a way to get around this without turning off the wi-fi every time? Because that seems kind of annoying to do every time I want to use Spotify.

I never toyed much with using the "offline mode," and it seems that could achieve the desired effect--if I plan out ahead of time what I want to listen to, of course.