According to mobile ad firm Chitika, the Verizon iPhone now accounts for nearly 12%, or 1/8th, of iPhones sold in the United States. The number comes after weeks of measurements through a live tracker that keeps track of mobile ads being served to iOS devices, and most specifically iPhones. Chitika reported last month that Verizon iPhones were accounting for 3% of US iPhones after 24 hours of availability. That figure led to speculation that several existing iPhone owners were switching from AT&T to Verizon, although neither Apple or Verizon have provided official sales number. Other sources reported Apple wasn’t willing to share any numbers due to sales below expectations. But, then again, that was last month and more new customers or AT&T iPhone users may have recently switched to Verizon, if Chitika’s stats are correct.

Since the launch of the Verizon iPhone, we’ve been tracking iPhones through our system and breaking down what percentage come from AT&T vs. Verizon. As of today, Verizon is up to 12% of all iPhone web usage, based on data from the Chitika ad network.

Apple has expanded its partnership with Verizon Wireless to new devices lately, such as the CDMA iPhone and the iPad 2, which comes with native CDMA integration in a WiFi + 3G model rather than a separate MiFi bundle as we saw with the first generation iPad. There’s no doubt we’ll see more and more from Apple and Verizon in the next months. It’ll also be interesting to see whether or not Verizon’s intentions to discontinue the unlimited data plan this summer will affect the device’s sales in any way, or if Apple will ever release detailed sales number since the Verizon iPhone went on sale on February 10th. [via MacRumors]