The iPhone 4

Do you own a phone that doesn't do much (except make calls), but would find sat-nav (GPS), social networking and email capabilities useful? If so then you should seriously consider getting an iPhone. Not necessarily an iPhone 4, as both the latest version and the iPhone 3GS have these must-have features:

3G Okay, this is a prerequesite for smartphones nowadays, but 3G is essential for decent mobile internet.
Wireless The wireless network interface means that you can use your iPhone around the home, for email/social apps, without having to keep checking your computer.
GPS Used by millions of sat-nav devices all around the world, GPS allows your iPhone to become location-aware.
Camera/Video The camera on the iPhone 4 is 5 mega-pixels and very good quality, which means you can ditch your separate digital camera on most occasions. The video function (with push-to-focus on the latest iPhone) is also decent quality and great for most situations.
Apps There are over a quarter of a million iPhone apps in the App Store, and it's surprising how many decent free apps there are. Limit your selection to apps that you know will serve a useful purpose, and you won't end up spending a fortune.
Super-easy interface Virtually all control is through the multi-touch touchscreen, which makes all sorts of apps an absolute doddle to use. No more need for a tiny keypad with fiddly navigation buttons; everything is on-screen swipey!
Push notifications Apps on your iPhone can notify you (with your prior permission) of important alerts.

I am already starting to find the iPhone exceptionally useful (if not esential) for varied duties such as web server monitoring, email and social networking, cycle route planning and as a cycle computer. What could you do with one?