Sheikh `Attiyah Saqr, former head of Al-Azhar Fatwa Committee, states that: In principle, i`tikaf is a Sunnah. It becomes obligatory once the person vows to make it. In this sense, when a person vows to perform i`tikaf, it becomes incumbent on him to do it within a certain span, if he specifies a certain time for it, if not it can be done at any suitable time. If a person fails to do that, he is to make up for it in case of obligatory i`tikaf and in the case of Sunnah i`tikaf, making up for it is recommended.
As for using cell phone, we can say that a person observing i`tikaf is recommended to forget about the allurements of this world and never occupy himself with it. In other words, using the cell phone should be limited and confined to his basic needs. Also, he can use it in fulfilling the needs of his fellow Muslim brothers.
If a person misses the obligatory i`tikaf, and also fails to make up for it, and neglects it till his death, then no one is to make up for it on his behalf. This is the view of the majority of jurists while Ahmad ibn Hanbal says that it is obligatory that one make up for it on his behalf.
As it’s permissible for a person to go out of the Mosque at any time, using cell phone is permissible in the Mosque, in the sense that as a person is allowed to get out of Mosque for his personal needs, he is allowed to use cell phone as long as it’s confined to his personal needs or for righteous deeds. It is reported that when one called him to fulfil his need, Ibn `Abbas, may Allah be pleased with him, rushed to him. As one of those observing i`tikaf stopped him, he said: “I have heard the Messenger of Allah, peace and blessings be upon him, saying: ‘To answer the need of your brother is better in reward than spending ten years in i`tikaf.