Hi, Lena!
My in-laws live out of state and my ds is 2 yo. We've always put the phone up to his ear even before he could talk so he could hear their voices. He loves to talk with Nana now
We have lots of pictures and include them in our play acting (ie, calling someone on the play phone). We see them 2-3 times a year and ds always knows them and is just as excited to see them as my parents who live just down the road and see him 1-2 per week!