That's right: Your phone can double as a flash drive. This is easier than you might think; here's how to make it happen:
Ingredient number one: a microSD card. (If you've never seen one before, they're astonishingly small -- about the size of the fingernail on your ring finger.)
Like other memory cards, microSDs are available in a variety of capacities. SanDisk, for example, sells 4GB, 8GB, and 16GB cards, with prices ranging from $31.99 to $108.99.
(Those are list prices -- they're way cheaper if you shop online. Amazon, for instance, offers the 8GB SanDisk microSD card, with an SD adapter, for $23.99.)
After inserting the card, connect your phone to your PC via its USB cable. It should get recognized as an external drive, just like a flash drive. Don't be suprised if you see two new drives; one is likely your phone's internal memory. (Some models make that storage PC-accessible as well.)
Now just copy your files over and be on your way. The only real downside here is that you need to bring along your USB cable so you can hook up with your other PC(s). Of course, the upside is that you can pack your card with MP3s as well as business documents, then let your phone sub in for your iPod. One less thing to carry!