Speed typing on a handheld device is so frigging difficult, especially if one has stubby thumbs. And if one is particular about the grammar, the spellings and the syntax even for text messages, speed typing with thumbs is hell. I so wish each of my thumbs had five sub-digits of their own - projecting in and out of the thumbs when near a handheld device. Mann that would make life so easy. I'd even rock the qwerty keyboards on damn Blackberries with their tiny little keys.
But evolution takes so damn long. It took us millions of years to get opposable thumbs. We should be glad that we have opposable thumbs. If monkeys hadn't liked to peel their bananas before eating we'd be doomed*. Its good that technology evolves way faster. Before my thumbs grow digits of their own we'll likely have devices in which typing of any kind will be rendered redundant. I wish I'd still be around to see that day.
*A question for creationsists: I wonder if it was in God's plan to give us opposable thumbs so we could type on a Blackberry, but to punish us he made them stubby. Hmmmmm. May be this is the "missing link" that you were looking for!