Sometimes helpful hurts

I frequent several websites (Cingular for example) that have a feature in their data entry forms for phone numbers that automatically jumps out of the area code, into the "first three", and then finally into the "last four". So you just type:

2346547890

and happily it fills out the form like

234 654 7890

However, what these technical luminaries fail to realize is two things:

1. Not everyone can touch type numbers (much less touch type at all)
   
2. The vast marjority of the forms on the web that solicit phone numbers either don't break the field in three parts, or don't have the fancy "auto tabbing" feature.
   

The result of this miscalculation is a customer experience that leads to the form being filled out like this:

234 ___ 654_

And if the final tab takes you into another field (say name). Your "name" happily starts out as "7890"

Frustrated the customer has a mess to cleanup, and if they're anything like me, they'll discover when "Helpful hurts" as they accidentally (despite now knowing) repeat the same mistake because the "tab" is in their fingers. This time slightly closer because they repositioned the cursor in the "first three" field so they have:

234 654 ____

With name still starting as "7890". Maybe I'm abnormal because I use the web ALL THE TIME, but I bet not, and I'd bet larger money that Cingular (and others) haven't user-tested this feature.