The image you can see in this story comes from an April 2009 FCC (Federal Communications Commission) document. It shows that a 250Gb Computer Entertainment system with the product number CECH-2001B has been supplied for testing. Above that listing is a product numbered CECH-2001A, it's a 120Gb unit.
Surely, these are PS3 Slims being tested? Yes, a 250Gb one as well as the released 120Gb one.
But no, the document refers to product testing being carried out on behalf of a company called Sand Dollar Enterprises, Inc, not Sony. But wait, Sand Dollar's address in Foster City is registered to Sony.
Three things of major interest here: firstly, the 120Gb entertainment unit cited in the test report doesn't have the same product code as the PS3 Slim as released (CECH-2000A). Secondly, the idea that there is also a 250Gb model in the offing could be a red herring given that, thirdly, Sony was apparently able to use another company name to legally get a consumer electronics unit tested by a US federal authority.
All that said, Occam's razor would suggest that, yes, despite a minor serial number difference combined with a mild change of address, there is a 250Gb PS3 slim out there.
The full document is available
here - but be aware that for some reason the FCC can't get its website sorted, so the doc will download as 'retrieve.cgi' - just rename it as a pdf and you have a little bit of history in your drive.
Sources:
Joystiq
Engadget
PS3news