If something is too good to be true, it usually is. If you're not being charged data, it's probably because you're on WiFi. I seriously doubt that when using data over 3G, you won't be charged (shouldn't matter whether you're rooted or not).
Don't count on one or the other actually being used unless you are in you are a mile from anyone else or in a place with a WiFi sign up. I have a friend who caught someone parked near his home using his DSL wireless internet. It seems that he didn't put a password in so anyone could use it. I bet when you weren't charged that you were near someone else's home or office and accidentally leeching off of their DSL service.
mmm these WiFi interfaces don't just randomly connect to any available WiFi network... you have to explicitedly tell it to connect to a particular WiFi hotspot... so no "accidental" leeching... of course a newbie might not be aware of the meaning of all the windows he's saying OK to...
If you uses Google map for directions via wifi (with data shut off) and then use gps to track your movements on the trip, will you consume data?
Google maps caches a portion of the map to your phone, then updates the map during your trip using data. There are offline maps which you can download a map of a specific region which will work with GPS. I had a really good app, but lost it and forgot the name since I installed froyo. I'm using an app called "mapdroyd" right now. It's not turn by turn but it is very accurate and works offline. You can download individual states.
no im sure the customer doesn't have wifi 24/7 but his phone was rooted with custom rom on it, im not sure if that made it work that way, cuz in another topic you can just change the QNC in the moto Q and you will have unlimited data from pageplus, so maybe the same is happening to the eris
I'm positive that I used data because I don't ever turn my data off and my mail is getting pushed every 5 minutes from my exchange server. I've also use Google map while driving but my data remain full for 3 consecutive months. Oh well, I am in Incredible now and I can see the data changes has soon as I turn it on.