I was thinking about this today, actually! I've recently started uni so I'm away during the week and come home at the weekend, and I have been delighted with the piggies' greetings!
I went outside as soon as I got home and I was met with a chorus of excited piggy squeals when I said hello!

The only other time I hear them so excited is dinner time! I used to wonder whether they just got excited to see me because they thought girly voice = food, but I'm now fairly certain that this isn't always the case (don't get me wrong, though, most of the time they do think FOOD

). They will only get excited at dinner time, or if they are in the run and hear the sound of my sandals (not entirely sure why they associate that sound with food as, nine times out of ten, I'm only going into the garden, not bringing them food!).
If they hear me speak to them, they all run to the bars and climb up on their back legs and squeal x) They respond differently to different members of the family, too. They get the most excited when they hear me, but don't bother if they hear say, my brother, because he doesn't have much to do with them! Freddie
always greets me enthusiastically, without fail.
As for trust...my piggies are trusting to the point of stupidity! They think that anyone or anything that approaches them must come bearing food so will immediately greet them with great enthusiasm. They must trust me and my Dad fully as they will quite happily settle down and fall asleep on our laps - often with their eyes closed, which I didn't realise was uncommon for a piggy!