I agree completely with Ruth. Being self-employed myself my iPhone has become invaluable for many of the reasons she's mentioned, but email and internet access are very useful when you need to access information on the spot - very useful when negotiating with clients etc. As a motion graphics artist I carry my reel around with me (along with music, films etc) so I can show it to prospective clients at the drop of a hat.

The camera's not too bad even though it's only 2 megapixels; it makes up in the quality of the CCD, and shows up my old Sony Eriksson 5 megapixel camera for the donkey it was. Hey - and you can edit video on the go!

It is expensive, but as a piece of kit which does a heck of a lot it's pretty much unbeatable.