iMessaging is going to one phone on multiple phone account

I have two iPhones that fall under the same account as far as phone and data service goes. I have never had to have two appleid's separately before but with imessaging on the iPhone 3GS that belongs to my wife, it is sending text messages that she sends and receives to my phone and her friends are seeing my e-mail address as the header for their text conversations instead of her number or name depending upon whether they have her established in their contact list. Will we now have to create her own appleid to fix this problem?