Targeting AT&T for complaints about coverage, or voice reception, or incomplete 3G coverage is accurate, all those charges are true, but the next thing in the argument needs to be compared to what? Verizon's voice is better, but it's not better because Verizon has put more money into their network or because Verizon is modernizing faster. Verizon's voice is better because they use CDMA instead of GSM. CDMA is higher power, uses fewer towers and has significantly longer reach than GSM, but GSM has wildly more capacity, does better at a bunch of lower level things like encryption, and handles data far better. Those commercials where a Verizon user needs two phones to do data and voice simultaneously aren't a joke, that's a real failing and it's not what iPhone users expect.
So, for the initial launch of the iPhone and its maturing AT&T needed the iPhone and Apple needed AT&T, thus AT&T was the only reasonable choice. Verizon wouldn't play ball, AT&T would and continues to, and the other carriers in the US are too small or financially unhealthy to be considered. But now we're past that, right?
Let's look at a market where you can get an iPhone with different carriers. Europe is the most obvious comparison market and iPhones are available from several carriers there, but there's a catch in Europe and that is that coverage is, relatively speaking, reliable and mature and the cell networks are homogenous. Yep, the networks all run on GSM and are more or less the same. In that case Apple had only exclusivity as a bargaining position and they used it for the initial run into the market and when it no longer served, Apple widened up to include other carriers.
But here in the US we still have CDMA and GSM, and the iPhone from its inception has been a GSM device. Sure, it could have a different radio in it and be used on a CDMA network, but it’s somewhat silly to expect Apple to create a CDMA phone that would be useful only for Verizon or Sprint in the US and essentially nowhere else in the world.
The sole incentive for Apple to create a CDMA iPhone would be to add Verizon as a carrier and Verizon has already made clear that though they would like to have the iPhone, they wouldn't like to have it so much that they would go to the lengths that AT&T has shown it's willing to go.
Bottom line? No Verizon iPhone in the world we currently live in.
For the future the question becomes a bit more open... Verizon is moving to a system called GSM LTE (Long Term Evolution). This version of GSM is not backwards compatible and CDMA phones can't use it, but GSM LTE is where AT&T has been going these last few years, so at some point in the not wildly distant future an LTE iPhone would be technically capable of running on either AT&T or Verizon's network, but by that point it will probably be an odd reversal of the current situation in that AT&T's present-day investments into its network will probably mean that AT&T will be the carrier with the better voice, data and coverage.
Well, still, if we might get a Verizon iPhone why won't Apple tell us? Apple won't comment on the possibility of an iPhone on any other carrier because it would damage the relationship with AT&T, have an effect on sales of iPhones, affect contracts already in play and potentially damage Apple's core business, which these days is actually phones...