The incident late Monday night occurred amid a recent escalation of the intense rivalry between the two companies. It was reported by CNET and confirmed by Legere on his Twitter feed.
AT&T's party followed its conference for software developers the same day, and featured rap act Macklemore and Ryan Lewis. Legere claims to be a fan.
T-Mobile US Inc., the country's fourth-largest wireless carrier, is based in Bellevue. Legere took the job of CEO in Sept. 2012, and has made a point of breaking with the wireless industry's status quo, in terms of personal style and business models.