For years, phone carriers have wanted to find ways to make it easy for mobile customers to buy things and charge them to their phone bills.

That has legitimate uses, like buying ringtones and apps, or even making political donations or financial pledges to a nonprofit radio station. But it is easily abused, in ways not always easy to spot: Consumers, for instance, could start getting text messages about sports scores or horoscopes for which they never wanted to sign up.

“As with 900 numbers, it’s ripe with potential for abuse, and in some cases that potential has become reality,” said Jan Dawson, an independent telecom analyst for Jackdaw Research.

Such practices returned to the spotlight this week when the Federal Trade Commission filed a lawsuit accusing T-Mobile USA of profiting from “cramming” — the tacking on of unauthorized charges that appear, often without a coherent explanation, on customers’ bills.