It's a great idea, but you have to test the particular model to see if it actually works. The T-Mobile Dash (running windows mobile) is a good example which you could find online fairly easily IME.
I'd like to be able to check my email on the run, and maybe look up a quick thing or two online. If I buy an unlocked cell phone with a browser and wi-fi, and just don't put a SIM card in it, could I use it for this wherever there is wi-fi access? Is this a dumb idea? Is there a cheaper way to do this? Seems like I can get an unlocked, wi-fi phone for less than $100, which is much cheaper than a netbook.