I ran into the same ordeal as you today. Here is what I discovered. there is no way through which you can view the yahoo chat history through the Yahoo messenger application, but you can view it through the Mail box. here is what you should do:
1. Click on the mail icon on your yahoo phone
2.Go to the email account which you used for the yahoo messenger.
3.Scroll down to the very last folder on the list there. You will find a folder called: Y! conversations.
4. Click the folder to open and you will be able to see all the chat history made via the Yahoo messenger application on the phone.
Hi guys as experienced the same problem these last days with my yahoo conversation history on my iPhone, ipad and on my android phone I tried all the day to find a solution. So the solution that I found is:
1. Login in your yahoo mail from the browser, not from the application.
2. Open the "Options" folder
3. Select "Go back to classic mail"
4. Select "Conversation" folder
I know it's not that easy as it was, but I guess it's the only way till yahoo fix the problem.
access your yahoo mail account where the Y! Conversations folder got erased. click on edit, then create a new folder with the same name - Y! Conversations. after saving it, the folder will not only get saved but also contain all your conversation history.