I had the same issue but I didn't switch phones. Just one day the reply option was gone. All I could so was save drafts. I could create new emails and send them fine. I couldn't reply to emails.
I did everything in the book and even tried some things I shouldn't of to fix this issue. Finally I deleted the user from BES and added them back in and then ran Enterprise Activation again and it worked from then on and has never happened again.