just for correction Quran was completed within the lifetime of prophet, there was a group of people who learnt Quran by heart untill it was compiled by Caliph Usman after 20 to 25 years later. I dont know from where this theory of 150 years came from.

From the lifetime of prophet people in masses have learnt Quran till today and perhaps thats is the only book that is learnt by heart, line by line and word by word.

Even today you can check it with any Hafiz the people who learnt it, even if some body is reciting it wrongly they will correct it.

I agreed with with one of the post above that this form should be used for the pure sake of discussion not for preaching.