Interesting insight Hobbit, but I have to disagree. Your response is logical and reasonable, but there is NOTHING logical or reasonable about women. I would love to approach women logically, things would go so much smoother, but this 'tactic' never works. I believe Jack Nicholson said it best when asked in the movie As Good As It Gets, "How do you write woman so well?" His response..."I think of a man and I take away reason and accountability."
Now, does this mean my response was the CORRECT approach, not at all, but I do question your post.
Another approach would be to tell her that buying credits is getting costly, and they need to come up with another way to communicate. Maybe this will motivate her to make more of an effort. Does this seem immature, dramatic, or like we're playing 'games', absolutely! Unfortunately, this is how the game is played. Relationships are a chess match, whether you've been together 6 weeks, 6 months or 6 years. I've been in an LTR for years now with an HB9 and I still have to move my chess pieces around from time to time.
A guys says..."You are very caring and (blah blah blah), but the fact you never initiate calls sometimes makes me feel uneasy. I want this relationship to feel balanced!" She HEARS..."I'm always calling you, why don't you call me...i want some attention too."
Now the guy looks needy and his status drops a few notches. Does this make sense, hell no...but this is women we are talking about.

Anyway, that's just my 2 cents...onwards and upwards.