Setting mobile phones to ring with a musical tone is reprehensible and haraam, and it is even worse and more haraam if that happens in the houses of Allaah, namely the mosques, because that is openly committing falsehood and haraam in that place, so the sin of the one who brings it with him is even worse in the mosque. It is known that the Prophet (peace and blessings of Allaah be upon him) stated that musical instruments are haraam, meaning the instruments that give these musical sounds. These mobile phones have these sounds recorded in them which is repeated every time a call comes to the owner of the phone.  I wonder what will be recorded in the record of deeds of those who make their mobile phones play music in the houses of Allaah during the prayer, and disturb themselves and others, and make the voice of falsehood and the musical instruments of the Shaytaan echo loudly in the houses of Allaah.  

Do they not fear their Lord and repent to Him and give up what they are doing and change this evil, especially when there is a permissible alternative in the other regular, non-musical sounds that they can choose for the phone’s ring? 

We should note that the ringing of the telephone, even if it is a permissible sound, should still be turned off before entering the mosque, so that it will not disturb the worshippers. 

And Allaah is the One Whose help we seek and to whom we complain. There is no power and no strength except with Allaah.