Sprint
A leased line is the most common way that users connect to their carrier's point of presence
It depends what carrier your on. Most of them are in the hundreds starting at $199.99 is my guess. You can check with your carrier on their website.
There are a number of forums that are popular for iPhone users. Some of the most popular forums are the "iPhone Forums", "MacRumors Forum" or the "iLounge Forums".
orange and blackberry
There are many reasons. The most popular is users are in different network groups.
Nokia currently has the most smartphone users but Apple is taking over with iPhone.
I am pretty sure Orange is a stronger provider based on it's coverage range.
Considering current App usage data released to the public, there are indeed people who are addicted to iPhone Apps. Users of iPhones spend the most time using Apps, compared to other smartphone users.
competetive access provider
Unplug the printer from the network.
Judging by the category of the question, I assume you are talking about the 3GS. The 3GS is GSM only and it is physically impossible to use most other American networks since the only other GSM is T-Mobile, and it uses AWS bandwidth and the iPhone can only access it's slow EDGE network, but even that requires a SIM Card.
Now, with the new iPhone 4S it is theoretically possible for the iPhone to be used on any mobile phone network worldwide. For GSM usage (I.E. Sim Card) the iPhone must be unlocked, and a MicroSim must be placed in the iPhone to work. For CDMA use, the iPhone must be flashed to a network, and then additional steps will most likely have to be taken in order for the iPhone to work. If you go to a professional phone store, that flashes, and unlocks phones, then they can do this for you. Also, if you plan to use CDMA, you must get a CDMA iPhone 4S, like one from Sprint or Verizon, then it may be flashed to another CDMA compatible network, or unlocked for GSM use.