Mothers and Cell Phones: How Often Do You Call Your Mother?

So. We all have mothers. Some of us are lucky to still have them around.

I am originally from the East Coast, which makes me one of the many Los Angeles transplants in town. With the majority of my family residing back East, there is a considerable distance felt between us. So, my adorable parents, specifically my mother, uses her cell phone to keep in touch with me. She calls me. We exchange text messages - which is quite a feat for her to master, if you know her.

On the occasion that I don't receive her call, she leaves voicemail messages to the effect of, "Okay, call me. Now. Right now." The tone of these messages, mainly irritation/nagging, doesn't motivate me to call her back. Thus, my decreased rate of returning phone calls. Not that there's anything urgent or any particular purpose for her call anyways. Most of the time it's just to make sure I'm alive and to hear me talk - which is awesome, I know, but I can't be all that spectacular 24/7. No news from her to report, and since I don't call unless there's news on my end - in conclusion, no real functionality to accomplish.

If I don't talk to her within a couple days she'll think something awful has happened and then start calling furiously. Love her to death, but it gets to the point where I just don't want to pick up my phone. Does anyone have this problem?

I pose these questions:
1. How often does your mother call you?
2. Should I chalk it up to, "I'm not a mother, so I just don't understand" ?
3. What do you suggest as far as how to respond to the excessive calling?