A woman who took a friend's sim card and put it into her own phone made calls to her mother and boyfriend and ran up a bill of more than £400, Truro magistrates heard.
When she was asked why she took it she told the police: “I don't actually have a reason.”
Before the court was Nakhara Fawn Jacques, aged 19, of Kersey Close, Flushing, who pleaded guilty to fraud with a mobile phone between December and January at Penryn.
Alison May, for the CPS, said the owner of the phone was used to paying £15 a month for it and when he discovered the Sim card was missing checked his bill and found it was £429.
He recognised some of the calls made to Jacques' mother's number as he knew her. Jacques was a friend of the family and had visited his home.
She later told the police: “I did nick it….I was in a mood. I had no credit.”
Graham Calderwood, her solicitor, said she was a vulnerable person on quite strong medication for depression, and was anorexic.
She had been feeling low when the Sim card was taken although she did not know why she took it.
Jacques was given a conditional discharge for a year and told to pay compensation of £429.89 and £35 costs and surcharge.