I just spent a few hours installing emulators on my phone. Got picodrive, antsnes, speccy, frodo and dosbox. The thing is, that I don't have a keyboard phone yet, so c64, spectrum and dos lose their point. But this was mainly a dress rehearsal. Pity about the size/screensize/battery life physics, e75 has 'decent' batterylife, but a e71 would have 'good' batterylife. (EDIT: bigger screen=more size for battery or worse battery life, cpu the same to an extent) The reasons I'm going this route are cost, battery life and keyboard. There might be some android phones cheapish like the cliq, but I'd rather not use them. I tried (had it for nearly a year, but I always did my gaming on the wiz or gp2x) the ZeeMote properly for the first time too. It's got an analog stick, but it's a decent controller to use with one hand. I played GridRunner by Minter, but found the rate of fire better if I clicked directly on the buttons of the phone. If someones with an all touch phone, you might consider the zeemote, it's only 20€ or so.
Some future plans: I've been eyeing video glasses for awhile, and with HDMI ports coming on phones it's possible to get decent resolutions out of them. And by decent I mean VGA, as that's the only affordable solution. Their main problem is that they're not opaque. In the end I think the setup will (once it materializes) have a phone in a jacket internal pocket HDMI cable running running to glasses to have audio and video, and both pockets with something like a bluetooth frogpad and a ZeeMote on the other side.
This is fully doable starting NOW, except for the opaque glasses and frogpad seems to have trouble.
And that's what I think the industry is going to go to. This is modular, with the least material to lug around and replace so the upgrade cycle can be fast and furious.