I learned some real interesting things about the minaret from my history book on the Ottoman Empire.
Apparently the opening of the minaret was initially made for the Imam to go up to it and say the call of prayer loudly. Back then, there was no technology of course and the high tower of the minaret made sure that the call for prayer could be heard from far away. I think there are some Muslims today who feel that technology has no place in Islam and refuse to use microphones and speakers in the mosque. There are some mosques where the Imam still goes up to the minaret and calls out the call for prayer.
The minaret also calls out "salat." This is a prayer which is said when someone passes away. So the minaret announces a death to the neighborhood and locality as well.
I also learned that during the Ottoman Empire, the very rich were able to build mosques. These people held high statuses or positions in the Ottoman government. You could tell the status of the person by looking at the number of minarets of the mosque. The mosques with the highest number of minarets were the ones built by the Sultan.