Great, thanks! Actually, most flights I will just use the 'generic' option, with the checkboxes ticked for SIDs & STARs active, but this is good to know. Maybe I should try to read the user manual from cover to cover...
Now I have the STARs Active box checked, behaviour is of course slightly different: I was told to approach at pilot's discretion and to contact Tower when established. I was hand flying a slightly tricky approach (an a321 into VNKT Rwy20, no glideslope), and being rather busy, I forgot to contact tower on this occasion.

In PF3 Mode 2, I assume I would have to tune to the tower frequency manually? (On landing and pulling off the runway, I got no further instructions from ATC, but I suppose that that was because I hadn't contacted the tower during my approach).