I don’t own a mobile phone, but so far as I know, there are none available with a built in Cone of Silence. Given the sorts of information divulged by people in public places via mobile, this is no particular hardship.
What is it about talking into a mobile that deludes people into discussing personal issues in public? If you turned to a total stranger and said “It won’t be long until your sister finds out about her husband and the woman next door” they’d likely slap you without hesitation. If you then pointed out that they had just shared that news with seventy other people, they’d probably call the cops and have you arrested for invading their privacy.
Transperth have done a rather good poster about this problem. Click on the rhyme to see the image.
You can find the full set at this link. (2015.12.01 – Alas, no you can’t; not any more. The link directs to another page.) This is Transperth’s second collection of rhymes; who would have thought a government department could produce such wit?