The iqaamah is the announcement of the start of the prayer, upon which all voluntary prayers must be abandoned, and is done in a similar way to the adhaan. The way to do the iqaamah is by saying:

اللهُ أَكْبَرُ اللهُ أَكْبَرُ
أَشْهَدُ أَنْ لَّا إِلَهَ إِلَّا اللهُ 
أَشْهَدُ أَنَّ مُحَمَّدًا رَّسُولُ اللهِ
حَيَّ عَلَى الصَّلَاةِ 

حَيَّ عَلَى الْفَلَاحِ 
قَدْ قَامَتِ الصَّلَاةُ قَدْ قَامَتِ الصَّلَاةُ

اللهُ أَكْبَرُ اللهُ أَكْبَرُ
لَا إِلَهَ إِلَّا اللهُ 

Transliteration:

allaahu akbar, allaahu akbar  
ash-hadu an-laa ilaaha ill-allah
ash-hadu anna muḥammadar-rasoolullaah
Ḥayya 'alaṣ-Ṣalaah
Ḥayya 'alal Falāḥ
Qad qaamatis Salaah, Qad qaamatis salaah
allaahu akbar, allaahu akbar
laa ilaaha ill-allaah 

Translation: 

Allah is the greatest, Allah is the greatest
I bear witness that none has the right to be worshipped except Allah 
I bear witness that Muhammad is the Messenger of Allah
Come to Prayer
Come to Success
The prayer is established, The prayer is established
Allah is the greatest, Allah is the greatest
None has the right to be worshipped except Allah 

The evidence for this is part of a length narration:

It was narrated that ‘Abd-Allaah ibn Zayd said:

”Then he went a short distance away from me and said: 'When the prayer is about to begin, say: Allaahu akbar, Allaah akbar; ash-hadu an laa ilaah ill-Allaah; ash-hadu anna Muhammadan rasool-Allaah; Ḥayya 'alaṣ-Ṣalaah, Ḥayya 'alal Falāḥ; qad qaamat il-salaah, qad qaamat il-salaah (prayer is about to begin, twice); Allaahu akbar, Allaahu akbar; Laa ilaaha ill-Allaah..."  [Abū Dāwood 499]