When you combine multiple lines of NTT docomo, please apply for "Ikkatsu Seikyu Service (single billing service)" of NTT docomo.

If you use some lines other than NTT docomo (NTT EAST, NTT WEST, NTT Communications), please apply for "Omatome Seikyu Service (combined billing method)" with the main line of "Ikkatsu Seikyu Service" of NTT docomo as your main line of "Omatome Seikyu Service."

Then you will be able to combine some lines other than NTT docomo as sub-lines.