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."
YES
You get faster internet then the original iPhone.
does the iphone 3 have to have internet to work.
You have to pay for internet usage anyway, that question is irrelavant.
Yes, it costs extra for the internet on the iphone.
Yes, you can buy international iPhone's version (a iPhone with out Internet) in eBay or amazon, some iPhone that sell outside U.S, is international iPhone' version. You can use it with any network that you like.
The iHome will charge and play the iPhone. Your iPhone must be in airplane mode to avoid interference when the iPhone communicates with cell towers.
no, only iphone with 3g or 4glte
The iPhone has its own Service Plan which has Internet included.
Yes You can charge a DS With your iPhone, you just need to jailbreak your DS.
yes, you can just use wifi access to use the Internet on your iPhone
for an iphone there's already an app called safari which is the internet