A PSP phone patent application that Sony filed back in 2006 has been unearthed recently.
It looks a bit like the DS and the application says it has a full touchscreen that could emulate the fascia set-up of the PSP, that is "complete with haptic tactile feedback to give the simulated buttons some definition during use."
To quote: Other details indicate that Sony Ericsson was thinking of making use of such a touchscreen-focused device to deliver unique Walkman, Cyber-shot and internet browsing interfaces to a mobile, too.
So effectively what we're talking about here is Sony Ericsson's take on the iPhone with a PSP thrown in.
What's particularly interesting is that the patent predates the iPhone patent being made public by one week, meaning the company had a chance at being remembered in history as launching a revolutionary touchscreen mobile phone before Apple. That's if it had bothered to go to market with the product, obviously.