I love Smartphones.. I was a Blackberry user for years before I switched to a 32 gb iPhone 3GS last May.. never been happier! My iPhone has replaced my netbook and other laptop for mobile everything. I don't have to carry them anymore. I can browse the web anywhere pretty much the same as I can on my netbook (only thing I'm really missing that I use is flash, but Youtube is on iPhone anyway if you want to watch YT vids and it does it very well). I even logged in to IRC here on my iPhone last night with a free program I found. I love having all of my email (including attachments and HTML), websites and forums I frequent, chat programs (all of them, Skype, MSN, AIM, IRC, Facebook, etc) all at my finger tips whenever I want. So many great non-internet applications on the iPhone as well; more than I could talk about. If you got the new iPhone as well you'll get iMovie and stuff too for on the go video editing. It's quite a cool device and it works very, very well. My BlackBerry would get overwhelmed pretty easily when multitasking and freeze but the iPhone has never given me a problem and I'm a lot harder on it with multitasking and running more demanding software on it. I love the thing.
For webbrowsing and basic tasks the iPhone can definitely replace all of those other things. The new camera on the iPhone (and even the old one on the 3GS ones like mine) is quite good for any pictures that will be for web use, and there are image editing programs for download as well. It takes decent video and as I said the new one has iMovie for editing, but there are other applications you can download too (on even the older iPhones). I can open, edit, and create word processing documents as well, and open various other office attachments (which comes in handy when showing someone something on a paper I wrote for class or when wanting to read some downloaded fan fiction, etc). One thing you'd want access to a computer for to make the best use it though is ripping CDs to put on it. You can borrow use a friends computer for this to keep it simple - very likely they'd agree too since they'd get to listen to all of your music as well since it would be stored on their computer as well. You also do software and OS updates via the computer so it's needed for that, and to download some larger (over 25 mb) applications require you to use a regular computer and then sync to the device. You don't have to do that often though. I think I've only had mine actually hooked up less than a dozen times since I've had it since May. You could easily get away with just making use of a friends computer once in a while if they are willing to let you have your stuff stored there (I still think they would since they'd benefit from it too).
So yeah.. in my day to day life away from the house my iPhone has replaced everything else (iPod, Netbook, etc) I used to carry for the same uses. It also lets me use MY webbrowser, MY favourites, and MY own connection when doing things rather than using the wireless network at school which is unreliable in connectivity, and has some security issues that have plagued computers there. Such a great little device. Make sure to buy an Otter Box for it though. I drop mine a lot, lol. With that otter box though it hasn't been the least of a problem with moderate drops and bumps.
As far as BlackBerry goes.. its very limited compared to iPhone. Biggest difference is web browsing which is slow on the BlackBerry (due to hardware not 3G, its the same 3G just a slower device), and limited - the web browser it has does not display pages well and many functions on websites do not work as they should. Safari on iPhone displays them like Safari displays them on any other computer minus Flash (which came from a dispute between Adobe and Apple so support for it wasn't included in Safari). iPhone's touch screen and controls are very easy to use and learn as well. Typically when doing anything on it you just natural "do" the controls the first time without thinking about it because it makes since (like turning pages in a book, or scrolling, or moving something around). Zooming in and out on web pages with your fingers is super sweet. <3 BlackBerry's music player is obviously rather inferior to the iPod function of the iPhone (saw that one coming a mile away lol). There actually isn't anything at all my BlackBerry did better or that I like more than my iPhone.. it's got to be one of the best things I've ever purchased. I absolutely love it and am super addicted to it. Oh! Charging! Can charge via AC outlet or USB (same cord). On very long days where I know I'll be sitting around on my phone for much of the day I take cable for it with me in my bag and just charge it up when I need to anywhere I am pretty much - wall, computer, etc. It charges very fast and the battery life is quite good on it. You can buy extra battery things for it as well to extend the life, have a backup battery to hook in to etc as well as car adapters etc (I don't need one though because my truck has a USB port). I use my phone wirelessly in my truck as well with my stereo's systems built in hands free system for safe phone calls from my head unit, etc. It's quite nice. I could do that with my BlackBerry too. Homephone? Not even needed if you have good cell phone service with AT&T anyway.
The iPhone is also a great GPS unit with maps (downloads via 3G no computer required) and other GPS features. Built in compass, maps, pin point locations, find things, etc. Very easy to read since its full colour with a wonderful display that is very clear.
It's got a lot more things too. Check out Apple's website.