The answer to this question depends on your gender;
1. If you're a guy, you should call about once or twice a month. (which seems reasonable)
2. If you're a girl, you should call any time from 3 times a week to 3 times a day. Girls like to talk talk talk talk and talk, even if they have nothing to say...
There's nothing you can do about it, it's your nature, lol.
My brother calls my Mom almost every day, and they talk for 20 minutes or so. I don't think I'll be able to keep up with that. That's why it's better to go to college close to home; you see each other, so you don't really have to "talk."