Do you need an iphone. NO,
Will having your own smart phone change your life. YES it probably will TBH Many folks cant see the point in smart phones until they get one, and only then realise the massive difference they can make.
I'm not a fan of blackberries, as they are business oriented, and I also like to go out in cold weather (when its cold, there is easy money to make in betting blackberry owners who can type faster....Its quite funny when they realise they cant type with gloves on lol).
I have an iphone myself, as they will always have more support, and more docking units made for them. I'm not a fan of apple, but some facts just cant be ignored.
You could however get an android phone on contract, and not only should you be able to get a better monthly deal, but you could also get the phone free upfront.
I do find it odd that some people say you will get bored of apps and they are only curiosities...Maybe they should buy more useful apps. I use my apps EVERY day, and sometimes several times per day (this would be the same with an android phone).
Just as a quick example. If I want to go walking sometime, I can look on my shift app to see when i am working or not. I can send my shift pattern to any of my mates (and I have theirs too) so I know in advance when they will be free, If we do decide to go walking together, we can email each other routes and photos (so its free as I'm not texting the pics). I can book any accommodation I may need while I'm out in the field, or even buy something there and then on ebay (along with paying bills etc via internet banking). If we go somewhere we have never been before, then we can use the phones full spec GPS, and the compass (silva type) too if needed.
At the end of the day, the phone will look up the nearest fuel station or restaurant, to grab some supplies on the way home. Once in the car it acts as a sat nav (and hands free obviously), and also has an app that lets me see traffic cameras on the motorway, so i can actually see how busy the road is ahead (in near real time). This often helps on long journeys, where there has been an accident up ahead, as i can see which junction is the best to leave by (as my data will be more up to date than I can get from the radio). For sleeping out, I can listen to the radio, or watch a film or tv programme stored on the phone, or simply relax by reading one of the books on it, or gazing at the stars or moon, with either the star or moon apps.
All these tasks only use a fraction of the apps on the phone. I do have silly apps too, but probably no more than a dozen or so, and stick to the ones I need for work, and outdoor pursuits mostly.
As an aside, I actually save more than my phones monthly contract each month, by having red lazer installed on the phone. It only takes a trip to the shops to buy a few bits, and with red lazers ability to show me the cheapest price for the goods I'm after, I will often either get a discount in the store there and then (such as price matching) or will choose to buy right then, but using the phone to buy over the net. As an example, I bought a DVD the other night. In the store I was in it cost £12.99, but the app showed it for £2.99 in another store, so I bought it via the phone instead, with an instant saving of a tenner. Do this three times per month, and the phone is kind of free!