Given the news about Verizon Wireless overcharging its customers by about $50 million, mobile phone users may be smart to examine their bills more closely.

About 15 million of Verizon’s customers were charged $2 to $6 fees in recent years for data that they didn’t use and hadn’t signed up to receive, the company said in a statement issued Sunday. Those customers will get credits on upcoming bills, and former customers should see checks in the mail.

These bogus fees came to light because of reports from consumers, according to the U.S. Federal Communications Commission, which said it has been investigating Verizon since January after getting consumer tips.

But how should consumers spot these kinds of bad fees? And are certain plans more vulnerable than others?

The details of the Verizon case may be sorted out by the federal investigation, but here are a few generalized tips for mobile phone consumers of all networks:

Know what ‘cramming’ looks like

Sometimes wireless network companies may try to “cram” small fees into their bills, according to a FCC fact sheet on the subject.

Consumers would be well served to know what these bogus fees tend to look like. That starts with knowing what kind of plan you signed up for. If you don’t have a plan that includes wireless data — which is used to get you on the internet, run many apps, check e-mail, etc — then one of the first things to look for is a “data” charge on your bill.

Also look for fees that sound unusual or vague. Line items like “service fee,” “service charge,” “other fees,” “voice mail,” “mail server,” “calling plan,” “psychic” and “membership” should raise consumer eyebrows, the FCC says.

(Read More: CNN)