wdEndOfRangeColumnNumber relates to tables as you have discovered however following that line of thought you could use instead the horizontal page position to determine where the cursor or range is e.g. as in the following function. The three figures are the horizontal page positions of the three left margins.
Code:
Function WhichPageCol(oRng As Range) As Long
Select Case True
Case oRng.Information(wdHorizontalPositionRelativeToPage) >= 72 And _
oRng.Information(wdHorizontalPositionRelativeToPage) <= 316.5
WhichPageCol = 1
Case oRng.Information(wdHorizontalPositionRelativeToPage) >= 316.5 _
And oRng.Information(wdHorizontalPositionRelativeToPage) <= 561
WhichPageCol = 2
Case oRng.Information(wdHorizontalPositionRelativeToPage) >= 561
WhichPageCol = 3
End Select
End Function