AT&T Mobility keeps pouring money into TV advertising and was the biggest spender among the four Tier 1 carriers in September, according to TV advertising measurement firm iSpot.tv, maintaining the top spot it had in August. FierceWireless has partnered with iSpot to bring you a monthly snapshot of the wireless industry's spending on TV advertising. In September, wireless carriers spent an estimated $169 million on TV advertising. AT&T scored the lead in the category with 35.5 percent of the total, while Verizon Wireless took second place at 27 percent and T-Mobile US came in third at 10 percent. AT&T and Verizon both have two commercials among the top five spent on any single ad in September, with AT&T's "This Is Big," supporting its All in One Plan, taking the top spot with $18.3 million. For more on the ads, check out this special report.