I use e-mail if it's nothing urgent, more of an FYI or here's some insight I had. I save voicemails for times when I really need to talk. For that, it's when I'm really upset, like if I keep crying about something that happened or just feel really awful and can't seem to make myself feel better. Then I'll leave a rambling, weepy voicemail and ask her to call (same with marriage counselor). I'd say I've done this maybe 6 times in the past 6 months or so, which is much more frequently than over the past 3.5 years I've been seeing her.