Praise be to Allaah.
The evidence from the Qur'an and Sunnah, and the comments of the Sahaabah (may Allah be pleased with them), indicates that singing accompanied by music is haraam. This has been discussed previously in the answers to questions no. 5000 and 43736.
As it is proven that singing and music are haraam, the Muslim should hate that which Allah and His Messenger hate and tell others not to do it.
The Muslim should tell singers not to commit this sinful action, because the Prophet (blessings and peace of Allah be upon him) said: Whoever among you sees an evil action, then let him change it with his hand [by taking action]; if he cannot, then with his tongue [by speaking out]; and if he cannot, then with his heart - and that is the weakest of faith. Narrated by Muslim.
Voting via mobile phone for a singer so that she can win the title involves a number of things that are forbidden according to shareeah:
It implies approval of sin, and approval of sin is itself a sin. Al-Qurtubi (may Allah have mercy on him) said: Approval of sin is itself a sin, hence both the one who does it and the one who approves of it are included in the punishment for sin and are both doomed.
Tafseer al-Qurtubi, 5/418
It is failing to forbid what is evil. Al-Nawawi (may Allah have mercy on him) narrated that there was scholarly consensus that enjoining what is good and forbidding what is evil is obligatory.
Sharh Muslim, 9/22
It is encouraging singers in their sinning and their disobedience towards Allah, may He be exalted. Allah has forbidden us to help the sinner in his sin, as He says (interpretation of the meaning):
Help you one another in Al‑Birr and At‑Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment
It involves spending money, whether a small amount or a great amount, in disobedience towards Allah, and The feet of the slave of Allah will not move [on the Day of Resurrection] until he is asked about five things: his wealth, from where he acquired it and on what he spent itâ€¦
Narrated by al-Tirmidhi, 2417; classed as saheeh by al-Albaani in Saheeh Sunan al-Tirmidhi.
Taking an interest in these foolish programs distracts the Muslim from what is useful to him in both religious and worldly terms, and it distracts from what is really in his interests, and it distracts him from Allah, may He be exalted.
With regard to the expiation for the one who does that, there is no expiation except that he has to repent, which means: regretting what he has done, giving up participating in such programs, and resolving not to do that again.
He should also strive to do righteous deeds so that Allah will accept his repentance. Allah, may He be exalted, says (interpretation of the meaning):
And verily, I am indeed forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them (till his death)
And Allah knows best.