Macro To Enumerate Cell Contents

I have attched a spreadsheet to try to illustrate that task I am trying to complete.
In the original data "HANDSET MODEL" in cell D3 contains 3 handset models separated by underscores. I would like to enumerate these so that each handset model has its own row(the underscores will not be needed in the final version). All other data in that row stays the same(cells A3,B3,C3,E3)

Once this has been done I need the macro to move down to the next row and enumerate the handsets in cell D4, on this occassion thare are four handset and the number will vary from row to row. The macro would need to be able to cope with a variable number of rows for the original data and variable amount of handsets in the D column.