Each week Ross Rubin contributes Switched On, a column about consumer technology.

Last week's Switched On looked at some of the reasons that a Verizon iPhone might not bring seismic shifts to the cell phone market or the balance of power between the two largest carriers in the U.S., focusing more on the AT&T incentive. This column discusses the carrier's current CDMA network and its multi-year transition to LTE, which could lower some obstacles to a Verizon iPhone.

While reports have asserted that a Verizon iPhone may ship as early as January and that a CDMA version of the phone will go into production in September, there are reasons to doubt that Apple will create a CDMA iPhone for Verizon Wireless. Verizon Wireless is a large carrier, but it's subscriber base is relatively small compared to the one that is served by having a single GSM device that Apple can sell around the globe. That massive audience creates certain scale advantages for Apple.

In addition, Apple has repeatedly avoided supporting "legacy" technologies, and most CDMA carriers have committed long-term to LTE, with some supporting WiMAX. Indeed, in an investor call last week, Verizon CEO Ivan Seidenberg downplayed the idea that the iPhone was coming to Verizon imminently, noting, "We don't feel like we have an iPhone deficit. We would love to carry it when we get there, but we have to earn it."

Besides, while there has been some work done on supporting simultaneous voice and data on a a CDMA network, Verizon --- or a CDMA-based iPhone -- might not be able to handle voice and data at the same time -- a feature that Apple and AT&T have promoted on television. For these reasons, Apple would likely wait at least until Verizon had a national LTE footprint. Seidenberg said that Verizon intends to have 90 percent of U.S. cities "covered" by the end of 2012.

Also, while Verizon's LTE will live in the 700 MHz band, which should offer good permeability of walls for in-building coverage, it simply takes time to bring any new network on par with coverage of the last one. That means that an LTE / HSPA iPhone that offered no CDMA capabilities would likely have better coverage on AT&T than on Verizon, at least in 2012.

In addition, as we have seen with the first 4G phones from Sprint, early LTE devices are likely to consume more power than their 3G counterparts, and Apple has a long history of delaying technology adoption in the name of better battery life. A few examples include picking EDGE over 3G for the original iPhone, delaying adoption of multitasking to offer a more energy-efficient flavor, and choosing USB or Bluetooth-based tethering as opposed to offering Wi-Fi-based mobile hotspot support on the iPhone.

Without a doubt, a Verizon iPhone would certainly result in both customers defecting (back) to Verizon from AT&T (and possibly attracting customers from other carriers as well), and the handset would sell well to Verizon's existing customers. All this would help drive iPhone sales and increase its market share significantly. But the picture of the real impact of a Verizon iPhone gets cloudier as we look further into the future, one that appears likely to appear a long time after January.