And there's no better way to get it than to jump into a typing tutor. We've seen one before for the iPhone, but reader Travis (thanks!) sent us a tip about TypingWeb.com's free iPhone tutor (just go to their site on your iPhone, and enter some information to create an account), and I was impressed by how smoothly it worked. During the Basic test, I moved pretty quickly-- a nice 36 words per minute. But on the Advanced test, they throw all kinds of things at you (including intentionally misspelled words, so you have to dodge Apple's corrections), and I dropped down to about 16 wpm.
Definitely worth a try. A lot of iPhone typing seems to be situation-- moving around in a car or bus, for instance, makes things a lot harder. But at least this will give you a ballpark figure of your typing prowess.