Continuing its impressive series of flashmob stunts, T-Mobile recently held an a cappella concert welcoming travelers arriving at London's Heathrow Airport. The performers bust out a diverse array of lyrics, ranging from Iggy Pop and Thin Lizzy to Mel Tormé and Etta James. Like most good corporate stunts these days, "Welcome Back" was clearly inspired by the merry pranksters at Improv Everywhere. But T-Mobile again proves that marketers can take someone else's idea to a higher level instead of simply rehashing it and calling the result a viral video. Hat tip to Bassem Dahdouh on Twitter.