Part of the iPhone thing for Verizon is that it's a double hitter in many cases. When I, for example, got the iPhone 3G in 2008 it was my first smart phone and I had to switch from Verizon to ATT. I had been with Verizon for nearly 14 years before switching to ATT. So, the equation hits them twice: once by losing a customer and second, when a single competitor, ATT, gets the one they lose.
I would expect Verizon to benefit from an iPhone because many of the iPhone customers will not hesitate to leave ATT behind when there is another carrier option. Android poses less of an impact because they draw customers from all carriers so it's not limited to a single carrier where the impact is much greater.
Going forward, if Apple refuses to increase the size of the iPhone it will continue to lose out to phone makers that produce a wider spectrum of phones of different sizes. In order to compete Apple will have to produce a phone with a significantly larger screen, but, at the same time, they will need to continue to sell the current sized phones. Jobs is on record for ridiculing the larger phones and when they release there larger phone I fully expect him to say they have done large the right way to get around his previous comment.
Brian