According to the FCC, AT&T Wireless has been cited for the most WLNP complaints:

"AT&T Wireless was cited in the most complaints with 2,297; Sprint PCS received 1,119 complaints; Verizon Wireless received 739; Cingular Wireless L.L.C. was mentioned in 699; T-Mobile USA Inc. received 625 complaints; Nextel Communications Inc. was cited in 332 complaints; Qwest Communications International Inc. got 195 complaints and Alltel Corp. got 119 complaints. "

Ouch!