I am new to android development and I am trying to find out how to send files over WiFi. I have failed to find any tutorials on the topic and was hoping you could help or point me in the right direction.
Sending files via Bluetooth is commonly done via OBEX, which, alas, Android 1 doesn't support. Google has improved Bluetooth for Android 2.0, but it's unclear as to how extensive the improvements are.
Another alternative would be PAN. Fedora 10 (Linux) automatically adds a bluetooth PAN device to the collection of network devices when it detects Bluetooth hardware (I'm using a dongle). However, I'm not optimistic that my current handset can run tcp/ip via Bluetooth.
When you network two computers (for networking purposes, a phone is a "computer", too), the normal mode of operation is that the network stack selects the interface(s) that it deems most suitable. This can be based on whether a path from one computer to the other is physically available and how "expensive" it is. You don't normally open an interface, you open a connection. So whether the phone opts to go via WiFi, the carrier's own data services, or both can vary. But the point is, since all that is transparent, the app doesn't need to worry about it.
An IDE is no substitute for an Intelligent Developer.