I have a Casio G'zOne Ravine 2 with Push-to-Talk. I have been told the PTT feature will no longer be available/supported on this phone after 10/1/16 due to "migrating our PTT platform to our LTE network. And I was told that I would need to upgrade phones to keep the PTT feature. Is this correct?? I like my Casio and do not want to upgrade.