It looks like Verizon Wireless did a pretty good job of grabbing some quick iPhone market share from AT&T last month. Verizon’s launch of the iPhone in February marked the first time AT&T has faced competition for iPhone users since the carrier first teamed up with Apple to launch the phone back in June 2007. Though Verizon ended up offering the iPhone 4, rather than a new version of the iPhone, they still had an edge with their phone since it was the first iPhone to support mobile hotspot functionality out of the box.Chitika Insights, which is the research arm of the Chitika online advertising network, stated on Tuesday that it was seeing stats indicating 12.7% of the iPhone users on its network were from Verizon Wireless. The next day, that share dropped to 9.4% indicating some interesting usage patterns of Verizon iPhone users, but Chitika Insights felt pretty good about estimating that Verizon iPhone market share is probably around 10% based on what it has seen over a period of seven days. Initially, there were indications that the 12.7% may have been falsely elevated due to a snafu with Chitika’s database, but the update today is that the database issue didn’t result in a different number being reported.Unfortunately for AT&T, now they face competition when it comes to 3G iPads as well thanks to the introduction of the 3G version of the iPad 2 which is available for both AT&T and the Verizon Wireless network. Verizon Wireless began offering the Wi-Fi version of the iPad last year bundled with a MiFi mobile hotspot, but the iPad 2 marks the first time a 3G model will be available for both networks.Read more at Chitika.Brian’s OpinionLet me be the first to note that assuming Verizon Wireless has an iPhone market share of 10%, it still means that AT&T enjoys a healthy market share of 90% so there is little chance AT&T will be throwing in the white towel anytime soon. The 10% number should be a warning to the carrier that they should do what they can to patch up any perceived leaks in the dam before there are greater losses. I think AT&T has done a pretty good job with that so far by adjusting data plans to closely match Verizon’s, but they should be prepared to get more aggressive if the market calls for it.I always believed that the predictions indicating Verizon Wireless would crush AT&T’s market share of iPhone users practically overnight was a bit unrealistic. AT&T has had an opportunity to “dig in” and retain its iPhone users over more than three years of offering the iPhone. What I believe is more realistic is a slow trickling of iPhone users from AT&T over to Verizon Wireless as subscribers finish their contracts. After all, the iPhone 4 just came out last year which means plenty of users will be on the AT&T network for at least another year and a half. Also, there are other Verizon Wireless users still in their contracts waiting for them to end so they can get their hands on an iPhone as well.I think we really won’t know how successful AT&T has been at holding off Verizon’s entry into the iPhone market for at least another 18 months. That being said, I find it hard to believe by that time Verizon Wireless won’t have more than 10% market share.