It all depends on what your looking for. If you looking for Edge, 3g then no its impossible. But it should allow you to use Wi-fi
Yes, you can use your iPhone 3G(S) to access the Internet if you have an available WiFi connection.
Yes. AT&T offers services that allow the iPhone to access the Internet wherever there is a cellular data signal. Or, the iPhone can connect to a WiFi network to access the Internet without the need of an AT&T plan.
No, you have to get the Internet package.
Yes you should be able to as you are using your internet connection and not your service providers internet service
Yes, Its part of the data plan package
It depends on your carrier. If your carrier is AT&T, it would add a Data Plan to your bill without further notice. According to the AT&T website: "AT&T is Apple's exclusive carrier partner for iPhone in the United States. An eligible data plan for iPhone is required. This data plan covers data usage in the United States and does not cover international data usage and charges. If AT&T determines that you are using an iPhone on your account without an eligible data plan, AT&T reserves the right to add an eligible data plan to your account and bill you the appropriate monthly fee."
It comes as part of your iPhone's data plan unless you only use the WiFi to access the Internet. The data plans start at $30 USD.
You cant you got to have a data plan.
Yes, its part of the $30-$35/month data plan.
No. Verizon requires a data plan for iPhones.
The iPhone is only available for AT&T and yes, there is an iPhone-specific data plan that is required. iPhone's that have been "unlocked" can be used with other carriers such as T-Mobile or Verizon, but even then an extremely large to unlimited data plan would be required (otherwise, you would have a LOT of overage charges since the iPhone is connected to the internet at all times).
If you have a legal iPhone with ATT service then you already have an unlimited data plan, as the iPhone is not offered without one.