The man had been taken to jail, where he now faces the death penalty.
Mr Stevens, 30, an Iranian who changed his name from Mohammad Husseinzadeh after renouncing his Muslim faith and fleeing to England, was a history and geography teacher.
He had already spent nearly two years in jail for his involvement, with his friend, in the Iranian Workers' Communist party. During that time, he said, he was tortured for three days, which included spending 24 hours hanging by his hands in a cell. Two of his friends were executed.
After receiving the mobile call, he immediately left the school, in the north-west Iranian Kurdish town of Sardasht (where Saddam Hussein's army dropped chemical weapons in 1987), and headed for a town near the Turkish border.
It was as well he did not return to his parents' house as within hours the police had seized his possessions.
He was smuggled into Turkey in a lorry and embarked on a two-week, 3,000-mile journey to England to claim asylum. Since then, for nearly two years, he has lived in Yorkshire, where he hopes to teach.
He has been recounting his story to secondary pupils. "I want to tell my story to young people because I want to show them we are the same as each other. We are all people," he said.
His initial asylum request has been refused by the Home Office, as most are, according to the Refugee Council. He is now appealing against the decision.
Unable to work, he has given talks in 15 schools, chairs the Leeds branch of the International Organisation of Iranian Refugees, and organises meals for the poor.
Roy Flesher, the assistant head of Mount St Mary's Catholic high school in Leeds, where Mr Stevens addressed a group of 14- to 16-year-olds last week, said: "The pupils started off uncertain, but by the end they were sympathetic.
"They were particularly shocked when he told them about his friend who was killed for possessing alcohol. That's way outside their own experience."
He added: "Young people can be easily influenced by negative stereotypes and misconceptions surrounding asylum-seekers. Now they are better informed."
Mr Stevens' other passion is table tennis. A former Iranian champion, he gave it up when he was not allowed to compete in the West. Now he plays for Leeds.
Teachers can contact him at email@example.com