How about swiping left or right (or any gesture really) brings up a new number/page for that number? I'd hate to see the clean interface get changed by another button.
I think swiping would fit better though, although there could be a lot of swiping happening if you've got a few counters.
Also, editable titles would let you name your counter.
Unfortunately I don't have an iPhone or any of the i-family gadgets.