you have to log on to your enterprise account (if you have cingular you have to goto www cingular com/blackberrystart) and login from there and change your pin, each bb has a specific pin for security purposes, then youll probably have to resend the book but it can take upto 24 hours for it, but sometimes its alot faster then that (from a desktop computer)
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.
Had this a few times recently, each one was a few days after upgrading from an old BB. (Usually from a 7730 to a 8707v). Seems like the service book can become corrupted if doing a full backup on the old device and a full restore on the new.
I have tried the suggestions above but in each case I had to wipe the handheld and start again. Still looking for a decent fix.
i found this to work although its not a direct fix... when you want to reply to an email, instead of selecting "reply" scroll down and select "email whoever" instead. You wont get any original text but it will allow you to send a reply