On Tuesday, September 27, Apple sent invitations for a press event to be held October 4, 2011, at 10:00 am at the Cupertino headquarters to announce details of the next generation iPhone, which turned out to be iPhone 4S. Over 1 million 4S models were sold in the first 24 hours after its release in October 2011. Due to large volumes of the iPhone being manufactured and its high selling price, Apple became the largest mobile handset vendor in the world by revenue, in 2011, surpassing long-time leader Nokia. American carrier C Spire Wireless announced that it would be carrying the iPhone 4S on October 19, 2011.