I don't have a mobile phone, but I've been using an iPod Touch for the last eight months, which has made me think about smartphones and "mobile computers".
The Touch came with the MacBook Pro which Camilla bought just before we left Australia. (Don't worry. The OS X install is still on that, but it's running Fedora Linux, we haven't gone over to the dark side!)
The Touch is basically an iPhone 3 with no phone capability - so dependent on a wifi connection for any networking. It's crippled - I haven't jailbroken it - but it supports a web browser and an ssh client.
- as a watch, since I don't have one of those.
- for emergency access to email and the Web (if I can find a wifi hotspot).
- for reading news on. It's much lighter than a book, and can be used one-handed, so it's neat to check the news (or the weather, or foreign exchange rates) in bed.
- for specialised apps. Apart from the ssh app (iSSH) the only one I've paid for is a "British Birds" app which provides pretty much what a field guide does but in a much more portable format (we often don't have a bird book when we want it) and also has recordings of bird calls.
- (possibly) as a travel computer, for email, booking hotels, etc., in place of my netbook (Acer Aspire One, first edition 8.9" model with SSD). It's painful to use, but is also much lighter and more compact.
- I haven't worked out how to get files onto or off it (using Linux) so I can't use it as a music player. (I should be able to do this, but Apple's insistence on proprietary interfaces is a real nuisance.)
- The storage isn't encrypted, so I'm unwilling to store contacts on it, or cache email or passwords. So if I want to read email, I use ssh, rekeying my passphrase every time. I really want encrypted storage, perhaps with some kind of biometrics + short PIN for access.
- The inability to multi-task makes it useless as a general-purpose computer. And I really miss having bash and Python.
So the iPod touch will remain a toy. For a proper mobile computer, I really want something that I control, which means a free software stack. Given that some Android phones are hardware rooted, and other concerns over Android, I may wait to see if MeeGo looks any good.
As far as hardware goes, I think a device 50% larger would fit my needs better - still pocketable, but the extra space would make web and ssh vastly more usable. A tablet is a possibility - if it's more robust and smaller than my netbook.