To the shock of very few, the advertisement about a week ago listing a "PSP-4000" in addition to PSPs 1000 through 3000, and the Go, has been disowned by the advertiser, who calls it an error.
Accessories4Technology, the creator of the ad (and the accessories series mentioned in it) told Negative Gamer that it was all "a mistake on our part." licence manager Angela Jones told the site that she wasn't sure how the error was made but, to her company's knowledge, Sony isn't working on a new version of the handheld.
Negative Gamer adds that Sony's response to the issue remains the standard no-comment for rumour and speculation, but I can't say that policy indicates anything other than what this is, an advertiser mistake. PSP-4000 Advert was 'Mistake' [Negative Gamer]