Sure they will eventually have as much power. But I doubt you'll ever be able to use them for serious computer work.
I have a pretty powerful PDA (Axim X51V) which I used to do emails on when I was travelling and could get wi-fi access, and while it was functional enough in a pinch, in fact it was seriously crippled compared to a PC. I would never have considered using it to write a document on. The screen real estate, even with proper VGA resolution, was far too cramped and typing was next to impossible on the rinky-dink little on-screen keyboard they provided. I could buy always buy a little bluetooth keyboard or so, but that would have meant more to carry around etc, etc. And those problems will always be there, no matter how much processing power and storage they manage to cram into phones/PDAs, just the size issue alone. It's an issue of touch-typing vs thumb typing, a 19 inch screen vs a 3.5 in screen, keyboard and mouse vs touchscreen and so on. The devil is in the details.
Not to mention that people on a budget are not going to be able to afford a phone with enough power to replace a PC. Pound for pound, they're better off just getting a computer with average specs.