What problem does the man mention?

M: Did you make any international calls recently? l just got our billing statement, and it’s a lot higher than usual. We were charged $150 this month.
W: Hmm, I don’t think I used the phone any more than I normally do. You should probably contact the phone company to find out what happened.
M: I noticed they charged us for incoming calls as well as outgoing ones. Maybe that’s what caused the bill increase.
W: You’re probably right. When we signed up for the service, I remember the agent saying that all incoming calls would be free. l can check the contract to make sure.