Telephones have evolved from fixed, expensive devices on wired networks to cheap, mobile devices on wireless networks. Our placement of calls has likewise evolved from reaching out to places to reaching out to inviduals. I used to call my grandmother at her house, so my intentionality was calling her house in hopes of reaching her individually or whoever else may answer. Calling my mom used to be like that, but since she relies on a mobile phone these days, the idea is like calling my mom's purse rather than her house. So when I call her I know the call is directed at her personally rather than her residence. That means she might answer while she is in a grocery store, and it means I'll have fewer conversations with my stepfather.
Sometimes, though, you don't want to reach someone if she is not at home. If she is not at home, she may be busy, and you only want to talk to her if she has free time and not bother her otherwise. Other times, though, you want to reach someone regardless of where they are, and it is disappointing if your only option is to catch them at home. So it is interesting to have two options to fit different moods and different reasons for calling.
I can't guess what the specifics might be, but it seems like mobile phones have an implication for our society in the way we reach out to people and where we talk to them. We're often calling people's persons rather than fixed places now.