SanDisk announced a 4GB Memory Stick DUO Pro at PMA on Sunday. The new chip doubles the previous best of 2GB. While it's being marketed to megabyte hungry digital photographers, it will also work fine in a Sony Ericsson Walkman branded phone. This will allow a current W800i or W900i to compete head-to-head with the Nokia N91 or iPod nano in storage capacity. No other cell phone maker uses the Memory Stick DUO format.
Sony Ericsson announced a music phone earlier this month that sports 4GB of internal flash memory, the W950i. It doesn't have a memory card slot for expandable storage.
SanDisk will begin shipping the 4GB card next month for an estimated $239.99.