T-Mobile CEO John Legere said on Thursday that his company, currently ranked as the fourth-largest wireless carrier in the country, will soon surpass No. 3 Sprint, if it hasn't already.

"For nine quarters in a row we have over 1 million [customers] added," he said in an interview on CNBC's "Squawk on the Street." "I'm pretty sure the yellow school bus [Sprint] is in the back."