Although I think that either a Sony or Nintendo branded phone is likely at some point, I just can't fathom how either would work. Take Nintendo - playful, mass appeal, family friendly. Where does a monthly subscription fit into all of that?
I don't know how the service end would be tied up with the hardware. One solution would be to have a subscription that allowed 'all you can eat' access to something like the Virtual Console, but then why not just make that an optional extra in a future handheld instead of a phone?
As far as a Playstation phone goes it would have to have one of two things; a UMD drive or direct access to the PS Store and an ability to play all of the content available there (i.e. PS! emu titles, download only PSP games etc). The problem here is that the PS Store would have to evolve into something much more robust in terms of content than it is just now.
Mobiles are getting better at their own type of gaming experience so do we really need to combine our beloved pocket gadgets that are designed to do different things? Is it convergence for the sake of convergence?
Like a tramp in the night, I'm begging for your love - Samantha Fox