Yes, you can, however, without service, all online features (calling, texting, internet, internet-based apps, etc.) will not function.
yes. eBay.
http://support.apple.com/kb/HT3406
There are multiple ways you can buy an iPhone. You can buy an iPhone online at the Apple website, a cell phone service company website, or on online shops like eBay or Amazon. You can also buy an iPhone at a retail store.
No. You can't activate the iPhone without activating service plan. If you are just looking for the ipod and internet functionality, you should consider the iPod touch
Many companies offer cell phone service without a contract that also offer and IPhone 4. Cricket, AT&T, T-Mobile, and even sites such as Best Buy and Amazon can offer these phone without a contract.
The iPhone has its own Service Plan which has Internet included.
Just like a regular iphone, but without calling or texting people/plans
Yes
Could be you just want a iPhone on prepaid
Ebay
Currently you can only buy the iPhone with a service plan. Part of the reason the phone price is low is that the service plan subsidizes the phone price. You could buy an iPod Touch, which is basically the same thing you're asking for, or you might be able to find a used iPhone for sale that no longer has a service plan. If you're done with the service plan and own the iPhone, here's how to use it as an iPod Touch: http://support.apple.com/kb/HT3406
You can buy one without an upgrade but it will cost you a lot more money