If you have an iPhone, you have the option to connect via 3G or via WiFi. Either way, you still get data connectivity. But there are a number of important differences between 3G and WiFi in iPhones. 3G connects through the cellular network of the provider while WiFi connects to a local hotspot and uses the hotspot’s internet connection.
If you are using 3G, you should make sure that you have an associated data plan; unlimited is better. You should also pay close attention to your usage or you might get an unwelcome surprise in your next phone bill. Using WiFi is not as complicated as you do not have to worry about such charges. Most internet connections are unlimited. Even the limited traffic plans do not charge exorbitant charges like most cellphone providers do.
The primary advantage of 3G over WiFi is coverage. 3G networks cover entire cities and you can move from one location to another without losing connectivity. Except of course in areas where buildings may hinder the 3G signal from reaching your phone. WiFi hotspots are not interconnected like 3G networks are. So if you move too far from the access point, you lose the connection. Of course, you can connect to another hotspot, but the transition isn’t smooth.
The downside of 3Gs range and coverage is the distance between the cell tower and your iPhone. While typical WiFi distances are within a few meters, 3G may cover a couple of kilometers. Increased distance requires greater power to transmit and receive data. In simple terms, using 3G drains your battery a lot faster than when you are using WiFi. It’s not a big deal if you are only using the connection for push email; but if you are going to browse the web or stream videos, you are much better off using WiFi rather than 3G.
Another consideration is speed. Typically, although it may vary, WiFi is able to achieve greater speeds than 3G connections. This will not hold true if there are a lot of people concurrently connected to the access point, like in public places like airports. But in homes and small offices, you will probably get better speeds with WiFi.
Summary:
3G connects through the cellular network while WiFi does not
3G may incur additional charges while WiFi does not
3G has a much greater range than WiFi does
3G will suck your battery faster than WiFi
WiFi is much faster than 3G