I just got my iphone and I did not activate it through AT&T. Instead, i hacked it using the method on this forum(not supersim method, just the one to make it work with other cingular sims) to make it work with my 39.99 national rollover plan.
Now there is a little E simple on the top left corner of the iphone, i know it is edge. But whenever I want to access googlemap, gmail, it always ask me for wifi network. However, when i click the settings, it said
edge network data:
send: 243KB
Received:1.7MB

So i am a little confused. I think i cannot use the edge after I hack the iphone in this way. Is there any way i can differentiate whether I am using wifi or edge? Coz if it is using edge, then i have to pay $.01/kB, which can be outrageous for 10MB data

If you are on EDGE, you will have the little E icon on the top of your screen. If you are on Wi-Fi, you will have an icon that looks like a triangle with 3 levels. If you have ever seen the Airport icon on a Mac, it's the same.

You are using EDGE, there is no way to turn it off easily. I use iPhone with Pay as you go (edge rates are ridiculous and no unlimited data option), called ATT and cancelled Media net completely, now phone doesn't connect to EDGE at all, which is what I wanted.
If you don't want to connect to EDGE but still want the data option on your plan (maybe to use with different phone), i suppose you can edit APN settings so it can't connect.