I heard this from recruiters when I was negotiating salary right out of college. "I want to give you more but we have a policy that unless you have another offer..."
I was more than happy to share, but we also already had a relationship where I knew he wasn't out to screw me.
Same as lying about your previous salary.
If you feel under valued, and talking to your boss doesn't get you a raise, why not just look for a new job? Doesn't cost you anything.