US Modular is going to offer memory expansion to Mobile phones with MicroSD or T-Flash slot.

The US Modular Stik & Stor uses a similar concept as the hard-drive expansion for the Sony PSP. It runs a short cable inside the MicroSD or T-Flash slot of the phone connecting a small unit carrying the storage. Phones like the Samsung D600 or Motorola ROKR are supported.
Bundled software lets you directly access the storage via a PC. I do not think the phones internal media players would work seamlessly with this additional storage.
The Stik & Stor is supposed to be available still this month. The 4GB ($149) and 8GB ($199) versions use a micro-drive. The 1GB ($79) and 2GB ($99) use flash memory.
More details on MobileTechNews and on the US Modular site. Via Slashdot.