"Verizon's about to take over as dumber from AT&T. I make that prediction," he told CNBC's "Squawk on the Street." "In next six months, they're going to do some stupid acquisition. Millennials still will hate them."
Legere said he believes Verizon has invested billions to acquire "junk."
The telecom giant purchased AOL last year for $4.4 billion, saying the acquisition would further its strategy to build out its LTE wireless video and streaming video strategy. AOL's advertising unit, which has outpaced revenue growth among its content brands, is also seen as a valuable asset.
Verizon is also believed to be on the shortlist of potential buyers of beleaguered internet portal Yahoo. Like AOL, Yahoo not only produces content, but is also a significant player in digital advertising.
"Verizon makes no excuses for investing in future growth," Bob Varettoni, executive director of media relations at Verizon, told CNBC. "Our goal is long-term shareholder value, based on a diverse and healthy cash flow. We use that cash to re-invest more than $17 billion in capital each year to provide customers with great networks, and great new services that take advantage of those networks."
Legere said he thinks Verizon wants to be in a different business, saying the company is seeking to attract millennials with video content offerings.
"That's not the business I'm in," Legere said. "We do mobile phone business. That's the core of what we do."
Legere made his comments after T-Mobile reported it swung to a profit and raised its 2016 forecast for customer additions, as competitively priced plans and free video streaming options helped it add over 1 million new monthly subscribers for the seventh-consecutive quarter.
Shares of T-Mobile were last down about 2.4 percent, reversing earlier gains.
T-Mobile has rolled out data-only plans, new family price offers and free music and video streaming services in recent months. Legere led the rollout of a series of consumer-friendly offers, such as the free video streaming option "Binge On," data rollover plans and social media campaigns in the past three years.
These have helped T-Mobile gain market share, as it is locked in a price war in an oversaturated wireless market with Verizon, AT&T and Sprint.
T-Mobile, controlled by Deutsche Telekom, said it added 2.2 million customers on a net basis in the first quarter ended March 31, surpassing the average analyst estimate of 1.72 million, according to research firm FactSet StreetAccount.
"We have had three full years of positive post-paid porting against the whole industry, and nine quarters of positive porting against everybody," Legere said. "They're all donating. Dumb and dumber are donating at record rates."
The Bellevue, Washington-based company said it now expects to add 3.2 million to 3.6 million postpaid customers on a net basis in 2016, compared with its previous forecast of 2.4 million to 3.4 million. Postpaid customers are those who pay monthly bills for the service.
Churn, or the rate at which subscribers defect to other networks, for postpaid users was 1.33 percent in the quarter, up slightly from 1.3 percent a year ago.
The company reported net income of $479 million, or 56 cents per share, for the first quarter, compared with a loss of $63 million, or 9 cents per share, a year earlier. This blew past analysts' expectations of 10 cents per share.
T-Mobile said revenue jumped 10.6 percent to $8.6 billion. Analysts on average had expected revenue of $8.43 billion, according to Thomson Reuters I/B/E/S.
To enhance its network capacity, T-Mobile has filed to participate in the U.S. government's auction of low-frequency spectrum, or airwaves, that kicked off in March. It has said it plans to spend about $10 billion in the auction.
— Reuters contributed to this story.