I recently deployed a series of 8821 wireless phones and came across certain issues with them, mainly connectivity issues etc. so thinking a firmware upgrade would fix it I went on ahead with it, only to find out that the phone(s) seem to accept the upgrade but immediately stop working and the center phone icon goes blank. I go back to the original firmware and phone begins working again. I tried different firmware upgrades and it does not make a difference. It will only work with the original firmware that is currently on the phone. I don't have any issues upgrading any other model phones. Any ideas?