The woman calling herself Tina rang the 28-year-old man on his mobile phone.
"She said she had found his number on the Internet and would really like to chat to him," a police spokesman in the westerly town of Wesel said on Wednesday.
She gave the man a number and asked him to ring her back, saying it would be a cheap rate. The pair then became locked in a six-hour conversation.
"The man said they talked about far more than just sex," the spokesman said.
Police are investigating allegations of fraud.