Enter subject for phone call to ease merging phone call tickets

About 8 months ago, Trengo has added the subject in the "merge ticket" popup. This, however doesn't work for phone calls, since a phone call ticket does not allow to enter a subject. Can you add the feature to add subjects to phone call tickets, so merging phone call tickets would become as easy as merging email tickets? 

Btw, in my opinion filling in the subject should be available for every channel available. Currently we use the internal notes to describe the content of a phone call in 1 line, but preferably we would like to type in the subject, so it works with merging tickets popup too.