The voice interface could be activated at a simple spoken request. But the main feature of the interface was the holographic avatar. It could take the form of anyone of the Doctor's choosing, (TV: Let's Kill Hitler) drawn from records kept in the TARDIS' memory banks. (HOMEVID: Meanwhile in the TARDIS)
It should not be confused with the actual TARDIS matrix, or soul, which only interacted directly with the Doctor once, after being placed in the body of a humanoid woman. (TV: The Doctor's Wife) According to the TARDIS, she was not constructed to allow her actual matrix to interact through the TARDIS technology.
Known interactions Edit
When the Eleventh Doctor was poisoned by Melody Pond, he accessed the voice interface as he was too weak to reach the console. It first took the form of himself, but he swiftly asked it to 'show him someone he liked'. Holographic projections of Rose Tyler and then Martha Jones and lastly that of Donna Noble appeared, but he dismissed all these avatars, as they made him feel guilt. The interface proceeded to take the form of a young Amelia Pond. This version of the interface informed him that it was the poison of the Judas tree and then spurred him into action, with the phrase 'fish fingers and custard'. (TV: Let's Kill Hitler)
In 1974, when the Eleventh Doctor disappeared in a pocket universe, Clara Oswald tried to save him by travelling to him in the TARDIS. It was locked, and the TARDIS activated her voice interface in the form of Clara because the interface was programmed to "select the image of a person you esteem." After talking to Clara, the TARDIS unlocked herself and let Clara save the Doctor. This was the first recorded instance in which the TARDIS activated her voice interface for someone other than the Doctor; in addition, it should be noted that Clara did not request it. (TV: Hide)