Thought this might be helpful, I bricked my own T28P following Yealink’s wonderful instructions on setting up OpenVPN, and after much pulling of hair and gnashing of teeth, managed to solve the issue without having to return the phone 
My phone was locked up, stuck on the dreaded “Initializing Please Wait” screen…
http://www.kellerdatacomm.com/yealink-vpn-initializing/
Hope this helps someone