Hm. Great question. I'll be interested to see how many others are like me, and how many are not.
I do not call my MIL. Pretty much at all. Unless I am returning a call or need to plan/discuss something specific. We get along just fine. But we aren't what I'd call "close". She doesn't call me either, though. She NEVER calls our house, and always calls my husband on his cell phone. Except when she accidentally calls MY cell phone thinking that it is his, and always sounds surprised that she got me instead. Or if I answer his phone, she gets all confused sounding.... lol. I "get" that with a lot of the younger generation. But she is pushing 70. The woman is of the generation that when you called someone, anyone in the family might pick up the phone. And she knows that we aren't possessive of our cell phones either.
I used to call my mom a lot. Not so much anymore. I always have other people around me, and for whatever reason, I don't like to carry on a phone conversation when others are around. It is weird to me. Like I have an "audience". I don't like it. Never have. So, since the kids or someone is ALWAYS around, I just don't make many calls... my mom included.
It's funny though, because my husband will sometimes call up my mom/dad just to chat them up, lol.