Here's a good tutorial on the how ROWSPAN and COLSPAN work, http://www.htmlcodetutorial.com/tables/index_famsupp_30.html
If you think of the table as an excel file that may help. Looking at your first row, (tr), you have 5 cells (5 tds.) None of them have a colspan so you have 5 columns in the first row. Old number is in your last column. So, if you want new number to be below it you have several options depending on how you want it to look.
You could have that single cell and colspan it 5 which means that one cell will take up all 5 columns. You then could align="right" so that the text is all the way to the right, so it lines up under the last cell.
However, a better approach, would be to put a td before your landline one and make it colspan 4 so that it fills up the first 4 columns. Then your landline would be the 5th column lining it up with old number (if I counted right).
It may help to use Excel to built it out first or possibly just draw it on a piece of paper. Even us experienced guys have to draw it out first sometimes to make sure it looks right visually.