OP, my DH is like yours. I do NOT bug him to call though-- it's his responsibility. And if they want to talk to him more often, they should call him. Which they do. It works out fine all around... if he doesn't remember to call them, they call us on the weekend.

Birthdays are also up to him to remember, though I've taken pity on him a little and started reminding him gently about those.