My mom calls when she wants to brag about something. She controls the conversation length by calling me from her car on her 5 minute drive home from work and ending the call when she pulls into her garage. At the end, she will stop talking, ask how we are all doing, I say good, and she says OK, gotta go now, just pulled into the driveway. Maybe about once a month or two.
I talk to my dad on the phone maybe a few times a year, but he and his wife are very active on facebook and we message back and forth all the time - at least a few times a week. If they weren't on FB, I would probably never go on it.
DH talks to his dad on the phone about once a week, and his mom once every few weeks. he texts her every few days just to check in and say hi