How to Call Adhan
Question

According to Hadith, how should one say the adhan? What are the real wordings? I mean one should say everything twice or once is enough.
Praise be to Allah.Versions of the adhan
Several versions of the adhan have been narrated in sound reports from the Prophet (peace and blessings of Allah be upon him). It is Sunnah to use all the versions that have been narrated from him in order to revive the Sunnah and to put an end to disputes and differences that may be raised by those who have no knowledge or who are fanatical about their own madhhabs. 
Shaykh Ibn ‘Uthaymin said: 
“Everything that has been narrated in the Sunnah about the adhan is permissible. Rather what should be done is to recite one version sometimes and another version sometimes, so long as that will not cause confusion and fitnah (tribulation). 
Adhan according to Imam Malik and Imam Al-Shafi`i
Imam Malik narrated seventeen phrases to be recited, starting with Allahu akbar, to be said twice; then the muadhdhin should recite the Shahadatayn to himself first, then say them out loud and continue with the adhan . 
According to Imam al-Shafi`i, there are nineteen phrases with the takbir at the beginning four times; then the muadhdhin should recite the Shahadatayn to himself first, then say them out loud and continue with the adhan. 
All of this was narrated in the Sunnah, so if you give the call to prayer one way sometimes and in the other way sometimes, this is better. The basic principle is that in the case of acts of worship which were narrated in different ways, it is preferable to do them in all of those ways.” (Al-Sharh al-Mumti’, 2/51- 52) 
Adhan according to Imam Ahmad and Imam Abu Hanifah
The madhhab of Imam Ahmad and Imam Abu Hanifah is that the adhan consists of fifteen phrases; this is the adhan of Bilal (may Allah be pleased with him). 
The evidence for the view of Malik and al-Shafi`i
It was narrated from Abu Mahdhurah that the Prophet of Allah (peace and blessings of Allah be upon him) taught him this adhan:
“Allahu akbar, Allah akbar, ash-hadu an la ilaha ill-Allah, ash-hadu an la ilaha ill-Allah, ash-hadu anna Muhammadan rasul-Allah, ash-hadu anna Muhammadan rasul-Allah. Then he should repeat, ash-hadu an la ilaha ill-Allah, ash-hadu an la ilaha ill-Allah, ash-hadu anna Muhammadan rasul-Allah, ash-hadu anna Muhammadan rasul-Allah. Hayya ‘ala al-salaah – twice; hayya ‘ala’l-falah – twice; Allahu akbar, Allahu akbar, La ilaha ill-Allah.” (Narrated by Muslim, 379). 
This hadith is the evidence quoted for the view of Malik and al-Shafi`i, because it describes two ways of reciting the takbir at the beginning of the adhan – twice according to the view of Malik and four times according to the view of al-Shafi`i. 
Al-Nawawi (may Allah have mercy on him) said: 
“This hadith in Sahih Muslim also mentions saying Allahu akbar only two times at the beginning. Elsewhere then in Muslim it says that Allah akbar should be said four times. Al-Qadi ‘Iyad (may Allah have mercy on him) said: in some reports in Sahih Muslim it mentions saying it four times. Al-Shafi`’i, Abu Hanifah, Ahmad and the majority of scholars said that it is to be repeated four times, and Malik said that it is to be repeated twice, and he quoted this hadith as evidence. 
The evidence for the view of Abu Hanifah and Ahmad
It was narrated that ‘Abd-Allah ibn Zayd said: When the Messenger of Allah (peace and blessings of Allah be upon him) ordered that a bell should be made so that it could be struck to call the people to prayer, a man walked around me whilst I was sleeping [i.e., in a dream], carrying a bell in his hand. I said, “O slave of Allah, will you sell this bell?” He asked, “What will you do with it?” I said, “We will call the people to prayer.” He said, “Shall I not tell you of something better than that?” I said, “Yes.” He said, “Say: Allahu akbar, Allah akbar, Allahu akbar, Allah akbar; ash-hadu an la ilaha ill-Allah, ash-hadu an la ilaha ill-Allah; ash-hadu anna Muhammadan rasul-Allah, ash-hadu anna Muhammadan rasul-Allah; hayya ‘ala al-salah, hayya ‘ala al-salah; hayya ‘ala’l-falah, hayya ‘ala’l-falah; Allahu akbar, Allahu akbar; La ilaha ill-Allah
(Allah is most Great, Allah is most Great, Allah is most Great, Allah is most Great. I bear witness that there is no god except Allah, I bear witness that there is no god except Allah. I bear witness that Muhammad is the Messenger of Allah, I bear witness that Muhammad is the Messenger of Allah. Come to prayer, come to prayer; come to success, come to success. Allah is most Great, Allah is most Great, there is no god except Allah).” Then he went a short distance away from me and said: “And when the prayer is about to begin (iqamah), say:
Allahu akbar, Allah akbar; ash-hadu an la ilah ill-Allah; ash-hadu anna Muhammadan rasul-Allah; hayya ‘ala al-salah, hayya ‘ala’l-falah; qad qamat il-salah, qad qamat il-salah (prayer is about to begin); Allahu akbar, Allahu akbar; La ilaha ill-Allah
The following morning, I went to the Messenger of Allah (peace and blessings of Allah be upon him) and told him what I had seen. He said, “This is a true dream, in sha Allah. Get up with Bilal and teach him what you saw, for he has a more melodious voice than you.” So I got up with Bilal and taught him, and he gave the call to prayer. ‘Umar ibn al-Khattab heard that in his house and he came out, dragging his lower garment and saying, “By the One Who sent you with the truth, O Messenger of Allah, I saw the same as he saw!” The Messenger of Allah (peace and blessings of Allah be upon him) said, “To Allah be praise.” (Narrated by Abu Dawud, 499; classed as sahih by Ibn Khuzaymah, 1/191 and Ibn Hibban, 4/572. al-Tirmidhi narrated that Imam al-Bukhari deemed it sahih, as it says in Sunan al-Bayhaqi, 1/390) 
Shaykh al-Islam Ibn Taymiyah said: 
“As this is the case, the correct view is the view of Ahl al-Hadith and those who agree with them, which is to accept everything that has been narrated from the Prophet (peace and blessings of Allah be upon him) and not to disapprove of any of these narrations, because the variations in the adhan and iqamah are like the variations in the recitation and tashahhud etc.… No one has the right to disapprove of anything that the Messenger of Allah (peace and blessings of Allah be upon him) has prescribed for his ummah. 
With regard to those who dispute and are divided on such issues, to the extent that they regard people as friends or enemies, or fight over such issues in which variation is approved of by Allah, as some of the people in the east do, they are among those who split up their religion (i.e. who left the true Islamic Monotheism), and became sects, [i.e. they invented new things in the religion (Bid‘ah), and followed their vain desires]  [cf. al-Rum 30:32]. 
In order to follow the Sunnah completely we should do it one way one time and the other way another time, this way in one place and the other way in another place, because forsaking what was narrated in the Sunnah and adhering to something else may lead to regarding what is Sunnah as bid’ah and regarding something that is mustahabb as obligatory, and that would lead to division and disputes if others do it the other way. 
So the Muslim should pay attention to the general principles which call for adherence to the Sunnah and the jama’ah (main body of Muslims), especially with regard to prayers in congregation.  
Saying the Shahadatayn twice in a low voice and then repeating that out loud in the adhan was the option favoured by Malik and al-Shafi`’i, but Malik thought that the takbeer should be said twice and al-Shafi`’i thought that it should be said four times, whereas Abu Hanifah thought that the Shahadatayn should not be said in a low voice during the adhan. With regard to Ahmad, he said that both ways were Sunnah but he preferred not to do it, because that was the adhan of Bilal. 
How to call iqamah
With regard to the iqamah , Malik, al-Shafi`’i and Ahmad said that the phrases should be said once, but Ahmad said that saying them twice is Sunnah. All three of them, Abu Hanifah, al-Shafi`’i and Ahmad, preferred to say Qad qamat il-salah twice, whereas Malik did not. And Allah knows best. (Majmu’ al-Fatawa, 22/66-69)
For more, please see this category: Call for Prayer
And Allah knows best.