Again, being that the iPhone is a new entrant into three fields simultaneously, it will be hard to judge how other companies plan to react/combat iPhone's presence. It would stand to reason, that most companies (Nokia, Motorola, and Blackberry Subsidiaries) would stand pat during the iPhone's introduction. If the product takes off, then the free-for-all will commence as each sector puts into effect their plans for counteracting the iPhone.
In my opinion, iPhone's partnership with Cingular will initially help shield iPhone from competitors who may have developed similar products but lack a promotional vehicle (i.e., a cell phone carrier willing to partner with and sell their product). All the other major cell phone carriers will not be able to "cash-in" on the iPhone craze if there is indeed a craze at all. The initial cost for interested parties to switch from their current phone carrier to Cingular and the iPhone is extremely cost prohibitive. Most cell phone companies have large fees associated with contract terminations and then you must add to that cost the fees associated with signing up with Cingular and buying an iPhone at $400.00 +. After iPhone's exclusive deal with Cingular ends, and provided that iPhone has proven to be a viable product, you will see other phone companies attempting to plug their services as iPhone compatible.
Form a mobile music standpoint; I definitely believe that the success of iPhone could eventually lead to the cannibalization of the iPod. In my estimation, there would be little reason to have an iPod if your cell phone does all the same functions plus keeps you connected to the world at large. What I am not sure is if this is actually part of Apple's plan. After all, it is always better to be the company that makes your own products obsolete than for a competitor to do so and effectively squeeze you out of the business.