I have just signed up for a free 30-day trial with Spotify Premium.
I was able to stream content at home (wifi), but am unable to stream once I left my house via 3G.
I have an iPhone 4, with Verizon service. I can see my playlists, and it looks like I should be hearing music. I can use other streaming services fine. I am not in offline mode.
Is this typical / expected?