messages
My dad has been trying to set up iMessage on my sisters iPod touch so my sister can text me. How do I sign in to iMessage on my iPod?
People have said to clear out all of the data, but we have not done so because all of the apps and contacts will be erased.
I managed to fix the issue by changing the following:
Settings > General > Date & Time > Set Automatically = On
As you can see in the first screenshot, you can set a number of email addresses by which you can receive messages at on your phone. However, as the second screenshot shows, you can only have one Apple ID connected to a device at a time.
You might be thinking, "Ok, can't I just add her Apple ID email address to my phone?"
The answer is no. Any time you add an email address to your iMessage account, the email is verified with Apple. If you attempt to add an email address associated with another Apple ID, Apple will decline it and neither iPhone nor OS X will not allow you to add the email address.
Conclusion: Unfortunately, there is no way to do this with iPhone or OS X. You could do what was previously suggested and set up a secondary account on your Mac (if you have one) and link that account to her Apple ID and use Message there to view the exchanges, but to specifically answer your question, OS X does not accept more than one Apple ID for iMessage per user and iPhone does not accept more than one Apple ID for iMessage either.
Best Answer
Go to Settings → Messages and log in with your Apple ID. This does not erase any data.