According to the article, in the case of cellphones:
cramming often begins when a consumer receives a text message with an offer to enter a contest. By replying, the consumer unknowingly signs up for a . . . service that provides the latest weather, traffic, news, sports or celebrity gossip. The charge for this “service” ends up on the consumer’s cellphone bill, often labeled as a “premium text message.”
In November 2013, the Texas Attorney General filed a lawsuit against four content providers behind a cramming scam, as well as a company that handled billing for cellphone carriers. Two weeks after Texas filed its lawsuit, “three major wireless carriers — AT&T Mobility, Sprint and T-Mobile — said they would no longer charge their customers for commercial ‘premium text messages,’ which account for the overwhelming majority of cramming complaints.”