I've had my treo for several months and just figured this out. In the phone application, if you have the preferences set to lookup contacts when you start typing, the phone will look up contacts but will also dial the number if you only push letter/number keys. So rather than having to choose a setting of looking up contacts OR dialing a number with the keyboard, you could do both and the Treo would automatically figure it out if you only pushed the letter/number keys and the letters made up gibberish.

For those of you who had the treo 270/300, that is they way the phone app used to work and I really missed this function on the treo 600.

Only problem is that the treo650 is a little slow in automatically figuring out contacts vs. numbers and sometimes doesn't get it right if you tap in the numbers too quickly.