SanDisk went and announced these 4GB Memory Sticks and 2GB SD cards today. Click the image below for the English press release. SanDisk is an American company, after all.

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By the way, this interested me because Sony hasn't even announced 4GB Memory Sticks yet. You'd think Sony, having invented Memory Stick, would be the first to make an announcement like this.
Now that we know the price of the PSP, and that it can play MP3s from a Memory Stick Duo, I suspect the demand for Memory Stick Duo will be o­n the rise in the coming months. Though SanDisk's 1GB Memory Stick Duo is set for $205 right now, I'm sure it will come down sharply.