Anyon know how Verizon's credit scoring works?

[jimbutsu]

Hi there-

I was wondering if anyone could shed any light on Verizon's ranking system for customers - it looks like once you're set up with them, you get a "Letter Grade" of some sort credit-wise. What do these mean, and how are they determined?

EDIT - no, before anyone asks, my credit is fine. I'm curious more than anything.