Is a PSP Phone just make believe?

It seems that Sony Ericsson's adoption of the make.believe tag line has prompted at least some commentators to call again for it to release a PSP Phone:

But Sony Ericsson’s only real hope for the long-term may be a PSP-branded phone that leverages Sony’s traction in the video game space. While the market for gaming-centric phones is questionable — see Nokia’s history with the Ngage — such a device could prove popular with a young, data-hungry mobile set. And it would be a better investment than a branding facelift.

There's clearly potential, as one of my colleagues, Brad Hagedorn noted a couple of months ago:

The potential for a PSP phone is clear when we compare the iPhone & iPod Touch’s growth with early sales of the PSP

Global growth of the iPhone, iPod Touch and PSP

Calling the iPod Touch a comparable, if less gaming centric, match to the PSP we see that their early growth is quite similar.  What is interesting though, is the gap between iPod Touch and iPhone + iPod Touch sales, which represents sales of iPhones.  Since the iPhone is essentially a Touch with phone capabilities, this gap is the oppotunity that Sony may be missing out by having a PSP, without having a PSP phone.