The call to prayer is recited not sang.
It is recited by the "muezzin" in the mosque. Just like the priest in the church, we have the "muezzin". I am not sure if your christian, but easiest way to explain "muezzin". There is a second call known as iqama (set up) that summons Muslims to line up for the beginning of the prayers.
There are five prayers a day, each one different timings of course:

1-Sobh(morning)
2-Zohr(noon)
3-Asr(afternoon)
4-Maghreb(sunset)
5-Eshaa(evening)

You can check this site to know more about it.
http://en.wikipedia.org/wiki/Adhan