apply textbox input to selected cells

Hi,

I'd like to know whether it is possible to input a text from textbox to a number of selected (non-contiguous) cells.
Basically, I need to write in a textbox, click on the related button and populate previously selected range of cells.
I do not know how to go ahead (from line ! onwards), other than just being able to input a pre-set text ("y" in my example) in the selected cells.

Range("I2").Select
    ActiveCell.Offset(1, 0).Select
    Do Until ActiveCell.Height <> 0
    ActiveCell.Offset(1, 0).Select
    Loop
    Range(ActiveCell, Cells(ActiveCell.Row + 3000, ActiveCell.Column)).Select
    Selection.SpecialCells(xlCellTypeVisible).Select
!   Selection.FormulaR1C1 = "y"

Thanks in advance.
Giuseppe