Curious, how big do people think this will be? Will Apple double its US userbase or will it be an incremental bump? I tend to think incremental.
The people in the US today who really want an iPhone have moved to ATT. The holdouts are those that:
1) Hate AT&T.
2) Are on a business plan who is tied to Verizon.
3) Those on a family plan, but aren't calling the shots.
For most of the people in 1-3, they already have a Verizon smartphone, and likely a relatively new one. So they'll trickle over the next year to 18 months.
Completely new accounts will go to the store and look at the phones. The iPhone looks less good, side by side, compared to the Droid X. With that said, there's no brand like the iPhone brand.
In any case, I think the sales on Verizon will be telling. Did people move to ATT to get the iPhone, or is there still tons of demand on the other carriers for the iPhone (obviously there's demand, but is it proportionate to the amount of demand that exists on ATT).