Conversation so far:
When was Erich Mielke imprisoned?
On 7 December 1989, Erich Mielke was arrested and placed in solitary confinement.
What crime was Erich Mielke convicted of?
After twenty months of one-and-a-half hour daily sessions, Erich Mielke was convicted on two counts of murder and one of attempted murder.
How long was Erich Mielke imprisoned in total?
Erich Mielke was incarcerated for 1,904 days.
What happened during Erich Mielke's imprisonment?
Erich Mielke was then put on trial while imprisoned for ordering the shootings of East Germans who were trying to defect to the West.
Are there any other interesting aspects about Erich Mielkes trial for shootings of East Germans who were trying to defect?
In November 1994, the presiding judge closed the proceedings for the trial of Erich Mielke, ruling that Erich Mielke was not mentally fit to stand trial.
What did Erich Mielke do after being released from prison?
After he was released from prison, Erich Mielke was obliged to move into a two room, 600-square-foot flat.
What else is interesting about Erich Mielke's imprisonment?
During his incarceration, at JVA Moabit corrections officers supplied Erich Mielke with a red telephone like the one in his office at Stasi Headquarters.

Question: What did he use the telephone for?
Self-contained rewrite: What did Erich Mielke use the telephone given to him by the Moabit corrections officer for?