Praise be to Allah.
The “Sada” service allows you to choose a particular sound that only the one who is making the call can hear. Some people choose this sound to be Qur’an, the adhaan, a du‘aa’ or a beneficial nasheed, and some choose it to be a song or music, and so on.
In principle, there is nothing wrong with this service, so long as the sound that the caller chooses is something permissible.
It is not permissible for this sound to be music or indecent songs, because of the proof that songs and music are haraam. This has been discussed previously in the answer to question no. 5000 .
With regard to choosing the sound of a qaari’ reciting Qur’an, this may be a type of disrespect towards the Holy Qur’an, because Allah, may He be exalted, sent down the Qur’an to be read, reflected upon, recited as an act of worship and acted upon.
The words of Allah, may He be exalted, are too great for us to make them simply a means of passing the time or to alert us to something.
Similarly, with regard to the adhaan, it was prescribed to alert people to the best and most important act of worship in Islam, namely the prayer, so it is deserving of appropriate respect and veneration. Therefore it should not be used for this service.
With regard to du‘aa’, the matter is more lenient.
Shaykh Saalih al-Fawzaan (may Allah preserving) was asked: What is your opinion on those who put the adhaan or recitation of the Holy Qur’an as ring tones on their mobile phones instead of music?
He replied: This is disrespectful towards the adhaan, dhikr and the Noble Qur’an; they should not be used as alarms, and the Qur’an should not be used as an alarm.
It may be said: This is better than music. Do you have to use music? Ignore music, and put some other sound that will alert you, in which there is no music or Qur’an, and it will simply alert you.
End quote from Majallat ad-Da‘wah, issue no. 2097.
See also the answer to question no. 34494 .
And Allah knows best.