Some cellphone users are eligible hundreds of dollars in refunds from their providers and U.S. Sen. Charles Schumer wants to make sure people have enough time to claim their cash.

The Federal Trade Commission reached a settlement with AT&T, T-Mobile, Verizon and Sprint following an investigation over an unfair billing practice known as cramming where some users received extra charges on their bills for ringtones, cell phone wallpaper, premium text messages, celebrity gossip or daily horoscopes.

Schumer said the agency should extend the deadlines to claim the refund and educate consumers on how to get their part of the settlement.

"The FTC should better publicize the practice of cramming and explain how consumers can apply for their well-deserved refunds," the senator said in a statement.

AT&T customers have until May 1 to claim their part of the a $105 million settlement while T-Mobile users have until June 30 to claim their part of the $90 million. Verizon and Sprint are still negotiating with the FTC over their settlements.

Customers can call 1-877-819-9692 for more information on the refunds.