Apple's iPhone 4 became available on the Verizon network in February. Photo: Jon Snyder/Wired.com

The iPhone appears to be gaining serious momentum on the Verizon network after just one month on the market.

About 10 percent of iPhone customers in the United States could be on Verizon, according to estimates by mobile advertisement firm Chitika.

If that estimate is accurate, it signifies rapid growth of the iPhone on Verizon. The Verizon iPhone went on sale online Feb. 3 for pre-orders, and the handset hit stores Feb. 10, ending AT&T’s exclusive partnership with Apple.

“For Verizon to pick up that big of a share of iPhone users in about a month is impressive, and doesn’t bode particularly well for AT&T,” Chitika said in a blog post.

Chitika has been using a live tracker to monitor web usage of iPhones on the Verizon and AT&T networks, based on activity of websites running ads on Chitika’s network.

The live tracker on Tuesday peaked at 12.7 percent of iPhones surfing the web on the Verizon network. As of Wednesday morning, the tracker shows 9.4 percent of iPhones are on Verizon. The results are based on 700,000 impressions from Chitika’s network.

“The spike is really interesting to me,” said Daniel Ruby, research director of Chitika, in an e-mail to Wired.com. “I’m trying to figure out if it’s indicative of a different usage pattern between AT&T and Verizon users, or if it was just a spike in Verizon usage across our network.”

Though Chitika believes the data presents a problem for AT&T, AT&T has said it’s not worried about iPhone customers switching over to Verizon.

AT&T previously told investors that it was confident iPhone profits would remain strong because many customers were on family plans and corporate plans, which would make it difficult to transition to a different network.

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