Yes, it definitely is cheating and dishonest, in my personal opinion. The OP is (or will soon be) ineligible for the discount that she is receiving. If she doesn't call Verizon to inform them of the change in her status, that is dishonest on her part. Whether or not Verizon decides to continue giving her the corporate discount after being informed of the change in employment status is an entirely different issue.
Here's another example: My son was a college student, and we were receiving a nice discount on our auto insurance because of that. He is no longer in college now. So, should I "forget" to call the insurance company so we can continue receiving that 10% discount? Or should I be honest, and call them to advise of his changed student status? Based on my responses to the OP's question, it should be pretty obvious which path I chose for our auto insurance.
I'm still rather amazed at the responses on this thread. If this person were cheating Disney by using a resident discount, misrepresenting a child's age for tickets, etc she would be raked over the coals. But being dishonest with a phone company seems to be okay with the majority of people who responded to this thread.