Jesus Prayer - with the mind or the mouth?

How often do we pray the Jesus Prayer throughout the day? Can we say it with our mouth or just our mind? The most holy St Kallistos, Patriarch of Constantinople, sheds some light on these questions:

 "Unceasing prayer consists in an unceasing invocation of the name of God. Whether talking, sitting, walking, making something, eating, or occupied in some other way, one should at all times and in every place call upon the name of God, according to the command of Scripture, ‘Pray without ceasing’ (1 Thess. 5:17).

In this way the enemy's attempts upon our life are foiled. We must pray with the heart; we must also pray with the mouth, when we are alone. But if we are in the market, or in the company of others, we should not pray with the lips, but only with the mind. We must keep watch over our sight and always look down to guard ourselves from distraction and the enemy's snares. Prayer has reached perfection when it is offered to God without the mind's wandering into distraction, when all a person's thoughts and feelings are gathered into one prayer."