I would think that the larger market would promote more sales. But IF not having an 'exclusive' contract for iPhone means Carriers are not able or willing to subsidize the hardware down to the current $199/ $299 price points, that would have a downward pressure on potential iPhone sales. But IF the new multi carrier market is such that competition for the customers seeking the new iPhone HD leads to subsidy level competition, then who knows where the subsidized price points will land.

But for me the multi carrier(s) aspect is less a factor (I think).
1) I currently have an AT&T package with two data plan phones. My wife's iPhone 3G is month to month. If the iPhone HD comes out June-ish, I'm thinking it will just be the GSM (AT&T) version. To change my service to Verizon 'when' a CDMA version is released (fall?), I'd need to buy two CDMA iPhones, one for each of us. If I plan to stay with GSM/ AT&T, I'd only need to buy one iPhone HD.

IF The CDMA version were to come out the same time (June-ish) as the new GSM iPhone HD, THAT would put me on the fence as to which way to go. Save money with one iPhone, or spend over budget to get two iPhones to get a better voice network. I cannot wait until we know some firm info on release dates of GSM & CDMA iPhone HDs. :o)