Well well let me think....
After we decided we were EXCLUSIVE ( I hope that is the word I am looking for) but anyway we answered each others house phone until we became ONE household. If you don't have anything to hide IMO it shouldn't matter. Don't have me flying across the room stumbling over tables, chair, kid, and toys and your behind is sitting right next to the phone....Pick it up and answer. NO Problem. The same with the Cell Phone. If you don't have anything to hide then let the Significant Other answer. I personally tell folks who ask Why is so and so answering the phone I politely tell when you start paying the bill then ask questions.
Email is private though the IHPE (inch high private eye) that I am I have his email password but I respect him enough to keep it that way but....you never know