I've had my iphone for only three months so I am far from an expert, but I do like it! My previous phone was a Sidekick, with a nice wide QWERTY keyboard which I will say was better not only for speed and accuracy in typing, but also because unlike the iphone, I didn't have to suffer from frozen fingers when using it outdoors in the winter. (Can't use the iphone's touch screen with gloves on.) Having said that, overall the iphone is a much more sophisticated device, fun and practical.
Apps? Here are a few that I have found to be useful, in no particular order. Zoyabean, some of these are for Londoners, but I hope you won't mind me mentioning them for the benefit of those who may be interested. And you'll be coming to visit London at some point, won't you?
London Tube Status (free): Tells you the current status of the tube lines, and perhaps more importantly, what closures are planned. Since there is so much construction going on, it's really essential to know before you go.
London Tube Deluxe (59p): A fancier version of London Tube Status (so you don't need both). Includes a system map and journey planner, and you can see upcoming departures at a particular station, with variable accuracy.
London Bus (59p): All three of these transport apps are from Malcolm Barclay by the way, just in case you get confused by other apps with similar names. This figures out where you are, and where you can catch a bus nearby to get to a destination you enter. Also has general info about all bus routes, such as how frequently the bus runs, but not a live update of when you can expect the next one.
Met Office Weather (free): Extremely detailed weather reports and forecasts. A new release, and often busy so if it doesn't work the first time you try it, just try again later.
Toiluxe Central London Edition (59p): Figures out where you are and locates "nice" toilets nearby. Moderately good now, but certainly has the potential to improve as users add to the database.
TuneIn Radio (119p): I use it to listen to BBC Radio 4 live, but you can choose from 30,000 stations, and record programs too.
Stanza (free): I like to carry a book with me to read on the train or during other down times, and an e-book reader is a perfectly portable solution. This app will let you download free copies of classics (I'm reading The Railway Children right now), or if you're feeling spendy, you can pay to download more current publications.
True Weight Lite (free): To track the effects of too much apple crumble and custard.
This American Life (179p): A new release and I am over the moon as this is my favorite radio program and the app gives you free yes free access to their entire archives! If you are a regular listener of TAL, you probably already know that you can download each week's one-hour program for free (subscribe via the podcasts section of itunes), but archived programs are 59p each. If you've never listened to TAL, please trust me, it's great. Each week has a different theme, and even if you don't think the theme sounds interesting, it's worth listening anyway because the stories are so compelling, funny, heartbreaking, etc. For the neophyte I recommend episode 230, Come Back to Afghanistan. It's one of my all-time favorites.
And two non-app tips:
Did you know you can add an icon to your home screen which will link you directly to the UK Yankee Forum? Yes, one tap and you are here! To do this, open Safari, go to the UKY Forum home page, scroll and size the screen how you'd like it to look (I recommend zooming in on the UK Yankee logo), and then tap the + (plus) sign at the bottom of the screen.
Although everyone says its easy to use the iPhone, I found that it was worth my time to borrow a guide book from the library, as I learned a lot of tips and tricks that I might not have figured out otherwise. The book I used was "The iPhone Book, UK 3GS" by Scott Kelby and Terry White, but "The Missing Manual" by David Pogue also looked good. Be sure to get the correct version for your phone model, or it won't be as useful.
OK, that was a long post, sorry! But I hope that maybe someone got something out of it. And I'm really excited to hear everyone else's tips for cool apps, I'm definitely going to check those out! Thank you Zoyabean for starting this thread!