My son and husband share the same Apple ID and have all the same media on both iPhones (games, itunes) etc. We are now experiencing a problem where my son receives all my husbands sent and received text messages through iMessage. I was told to change the Apple ID on my son's phone to his own so he would no longer be receiving the messages. When I change the ID, will he lose all of his iTunes? That is his greatest concern. Thanks.
The good news is that iOS allows you to have a separate iMessage Apple ID then your iTunes store Apple ID. To remedy your problem follow the steps below:
After this is done, you can go to Settings.app -> iTunes & App Stores, and make sure the Apple ID there is set to your Apple ID.
And, to firmly answer your question: No, having a separate Apple ID for iMessage and iTunes (and the process of changing it) will not erase content.
Note: instructions provided work best with iOS 6, but should be workable with iOS 5.