[BigV]

another consideration is how you're connecting to the internet.

earlier, up-thread, someone mentioned "wi-fi". in the context of the post, I think they meant internet access via phone while wandering around. strictly speaking, "wi-fi" is wireless internet via a wireless access point, like you might have in your home or at a coffee shop. At least, that's the way is it around here. the other way to reach the internet via your phone is via the cell phone network. It is that network, sometimes called "mobile data", that counts against the 500 MB / month data limit.

Where possible, connect to wi-fi (don't know what it looks like on an iphone, the terms/screen/etc), and save access to the internet via cell phone networks for when local, wireless networks are unavailable. this will help conserve your data usage.