AT&T said it surpassed 1 million iPhone 4S activations on Tuesday, making it the most successful launch despite its availability on two other carriers.
The Dallas telecommunications giant hit the mark after five days of sales.
The figure underscores AT&T's continued strength even as Verizon Wireless and Sprint Nextel offered the iPhone as well.
The company earlier reported third-quarter results that were in line with expectations. The iPhone 4S sales, however, aren't a part of the results because the phone launched after the end of the period. It activated 2.7 million iPhones in the third quarter, and Wall Street expects a surge in activations in the fourth quarter.
AT&T has a large base of iPhone customers who were able to upgrade their phone.
The AT&T version of the iPhone 4S is the only one compatible with HSPA+, an upgraded version of its 3G network it calls 4G. The Verizon and Sprint versions of the iPhone only run on the 3G network, despite offering 4G services.