Transflash or microSD or whatever you want to call it is quite tiny. Enter Stik and Store, a sticky memory key with a thin tape lead that ends in a T-Flash card. You can add up to 8GB to your phone by installing this thing just like an internal flash card and then threading the tape to the outside of the phone. It's a very kludgey solution—I see this ripping off in seconds—but if you need the memory it's one way to get around T-Flash limitations.
4GB and 8GB microdrive versions are $149 and $199 respectively and the 2GB flash version is $99.