Question: Oh Virtuous Shaikh, what is the ruling on using cellphones or the telephone in the masjid for the one in ‘Itikaaf? And what are the principles for that if it is allowed?
Answer: “There is no harm in using cellphones and telephones in the masjid for the one in ‘Itikaaf if he does not disrupt the people. If it disturbs the people then it is not allowed because the Prophet (ﷺ) came out to his Companions one night and they were praying in the masjid separately and reading loudly. So he said:
لا يؤذين بعضكم بعضاً في القراءة
One should not trouble the other and one should not raise the voice in recitation or in prayer over the voice of the other
[Reported by Abu Dawood and others. Graded Saheeh by Al-Albani in Saheeh Abu Dawood no. 1332]
So he ordered them not to recite aloud so as to not harm each other. So if these cellphones or pagers disturb the congregants, then it is obligatory for a person to silence it and turn it off so as to not distrub his brothers.
In this appropriate [time] I wish to mention to my brother Imams who pray over the Microphone and open it over the parameters of the masjid or in the minaret, that this disrupts those who are near the Masaajid. It disrupts the residents who are praying by themselves. Sometimes it leads to harm against the residents. A sick person may desire sleep, but [because of this] the sleep leaves him and he is harmed by this. So I call my brother Imams to close the microphones on minarets at the time of prayer because it harms without doubt. There is no benefit for the congregants because they are sufficed with loudspeakers inside, nor those outside the masjid. When those outside the masjid hear the recitation and they think the Imam is near ruku’, they run and rush to catch the ruku’ and oppose the Sunnah by that. It was complained to us, that some people remain in their homes and say: I will catch the prayer. Then he remains until one rak’ah remains of the prayer. So [sometimes] he catches the rak’ah and [sometimes] he does not catch it”.
[Taken from: https://shamela.ws/browse.php/book-7686/page-2067#page-2067]
Faisal Ibn Abdul Qaadir Ibn Hassan