Note that among the Ibadi madhhab there's a difference of opinion between the Ibadi's from al-Mashriq (for example 'Oman) and those from al-Maghrib.
I found the following statement from a 'Omani site:
The adhan of the Ibadi madhhab is more likely to that of the hanafi and shafi'i school
- Allahu Akbar, Allahu Akbar (2 times)
الله أكْبَرُ الله أَكْبَرْ الله أكْبَرُ الله أَكْبَرْ
- Ashhadu an laa-Ilaha illa Allah (2 times)
أَشْهَدُ أَنْ لا إِلَهَ إِلا الله أَشْهَدُ أَنْ لا إِلَهَ إِلا الله
- Ashahdu anna Muhammadan rasul-u-Llah (2 times)
أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ الله أَشْهَدُ أَنَّ مُحَمَّدًا رَسُولُ الله
- Hayya 'ala as-Salah (2 times)
حَيَّ عَلَى الصَّلاةِ حَيَّ عَلَى الصَّلاةِ
- Hayya 'ala al-Falah (2 times)
حَيَّ عَلَى الْفَلاحِ حَيَّ عَلَى الْفَلاحِ
- Allahu Akbar (2 times)
الله أَكْبَرُ الله أَكْبَرْ
- Laa ilaha illa Allah (once)
لا إِلَهَ إِلا الله
This wording is used for the call of all prayers.
As for the iqamah you it is similar to that of the hanafi madhhab as in it we use the wording of the adhan above but add:
Qad qamati as-Salaah (2 times)
قد قامت الصلاة قد قامت الصلاة
before the last two takbeers (step 6 above).
Note that the adhan and iqamah are most correct if they are performed in natural voice, and for the adhan especially it should be quite -with small pauses- and clear voice (which is also preferred by imam Malik), not in a melodical voice as is usually done in the middle east for example. While the iqamah has to be said without pausing and quicker. As for the adhan a natural prolongation (madd of two tones) of the words is recommended, but not in the iqamah so that it might be done quickly.
This is based on the book Ma'arij al-Aamaal of the imam as-Salimi معارج الآمال للإمام السالمي (See also here Volume 3 page 432). Note that tarji'i (saying the two shahadat step 2 and 3 first in a lower voice than repeating them in a louder voice) as is quoted in books of the maliki and shafi'i madhhab or saying "As-Salatu khayrun mina nawm" (at fajr or sobh time) or speaking during the adhahn is disliked.
This site from (Tadart Ibadi in Algeria) al-Maghrib has a totally different view and added sources and quotes the words of the Adhan as follows:
«الله أكبر الله أكبر، أشهد أن لا إله إلاَّ الله، أشهد أنَّ محمَّدا رسول الله، حيَّ على الصلاة، حيَّ على الفلاح، الله أكبر الله أكبر، لا إله إلاَّ الله».
Here the differences to that quoted earlier:
- Allahu Akbar (2 times by the people the Ibadis from al-Mashriq and 4 times by the Ibadi from al-Maghrib)
It is also said that step 4 is said to the right while step 5 is said to the left, without turning to either side. Ibn al-Qasim reported that imam Malik also strictly rejected turning left and right while performing adhan and he reported that he (ibn al-Qassim) witnessed the Muadhin's in Medina always facing the qiblah while performing adhan without turning to either site.
Note that adhan must be performed at the beginning of the time with two exceptions before fajr and the first adhan of Jumu'ah can be performed earlier.
See also: What theological and historical factors distinguish Ibadi Islam from either Shia or Sunni schools?