This has been discussed in many forums over the years and it seems there is no way to do this without writing code. I would like my contact form to have three grids - emails, phone calls and appointments. It is unrealistic to expect all activities to be marked as regarding a contact because in many cases the activity should be regarding a campaign or another activity. The timeline control is aware of related activities through the activity party list even when regarding is not set but this functionality does not extend to sub grids. It is seemingly not possible to have multiple timeline controls, each filtered on a different activity type.