Hey Belle_8015, I too use an iPhone, but have not really paid too much attention to these same things. iMessages is an Apple service, and not something we would have those specifics for. The great news is that those green messages are sending over Verizon instead of iMessage, so your normal text messages seem to be working. For additional support with iMessage, please contact Apple for support here: https://support.apple.com/contact
-Joseph