etymologyidioms
What is the origin of the idiom on the same page?
This is the definition of the idiom from Wiktionary:
In broad agreement or sharing a common general understanding or knowledge (common in office environments). I want to make sure we're all on the same page with the game plan for the Acme account.
I'm partial to the shift key+z typo answer.
If you're typing OMG really fast (cause you're so excited) you're going to slip and hit zOMG, since the < key isn't between shift and Z on most US keyboards.
Outside of any of the other possible origins, the typo is the most likely because it's most easily 'discovered' by small groups of people who are instant messaging each other. Most likely it has risen out of a parallell evolution because of our natural tendencies (as opposed to being invented or "first coined" by anyone).
Essentially, we all invent it ourselves.
It's a metaphor. Take the literal meaning and apply it figuratively to the situation.
Best Answer
This is the first citation of the phrase in the OED:
The next citation, which uses the phrase in its current form, is from 1979:
It was doubtless used in speech even before, and the paucity of written references is, I think, due both to the fact that it originated so recently and to the fact that it might have been considered slang at the time. (The OED categorizes it as colloquial, being used chiefly in the United States, and slang.) The first sentence, I think, makes somewhat clear the motivation for using such an expression.