I saw your post regarding setting up iMessage to only use email addresses so that you don't have issues when switching between your nexus 4 and iPhone 5. I may do the same thing but I have a question.
Since you don't associate your phone number, does that mean when other iPhone users send you a "text", it doesn't come through as an iMessage when you are on your iPhone? Meaning the only way to get iMessages on your phone is to have your other iPhone friends send their "texts" to your email address? I have friends who don't know the difference, they just "text" me (send messages to my phone number). When I'm on my iPhone, I want those messAges to come through as iMessage and when I'm on my nexus I want them to come as texts. Do you know if what I want to do is possible? Sounds like I'm going to have through go through the work of removing my phone number from the iMessage account whenever I want to use my nexus for it to work as I want.