- You cannot turn off data access on the iPhone 3G. Like Eurisko said, you must call Rogers / Fido and block the internet. You can turn off the 3G to save battery, but edge is still active.
- All apps will work over Wifi. The only thing I can think off that won't work is the GPS. Actually, it will work, but you just can't go very far because you need to stay connected to the wifi for google maps to load, which pretty much defeats the purpose.

There are some add-on apps that require an internet connection to work properly, so you would not be able to use them outside of wifi. There aren't very many though... and you can just avoid them.
- Just throwing this out there: The main difference between the original iPhone and the 3G is that the 3G has 3G and GPS. If you're not going to use the 3G aspect, then you're probably not going to use the GPS either, in which case, maybe you would consider a 1st gen iPhone? Personally I liked the feel / build of the original iPhone better. Also the battery lasts significantly longer. But I use the 3G and GPS every day, so it was worth the upgrade. But if I didn't want to use data through the cell network, then I would probably choose the original iPhone over the 3G. Just my 2 cents
