Hello again. Thanks for clarifying the situation.
It sounds like you have two separate situations: (1) your termination which was based upon the voicemail, and (2) the racial discrimination in the form of the failure to give you a raise because you're black (I assume that non-black employees doing the same work as you with roughly the same experience are being paid more).
First, the termination, I'm sorry to say, sounds like it may have been legitimate if it was truly due to the voicemail. You wrote that the Workplace Violence Prevention Policy "prohibits actions or words that ... result in that individual having a reasonable belief that he or she or someone else is in danger." Note the language that I underlined. This is important because it means that your motivation in stating the words is irrelevant. What is relevant is the recipient's reasonable belief. If you stated something that led the co-worker to reasonably believe that he was in danger, then it doesn't matter if you were intending to keep the peace or just speaking generally. Ultimately, only a court can decide whether it was reasonable for the co-worker to feel threatened by the voicemail, but it doesn't look good based on what you wrote here. I think a lot of people would likely feel threatened if they were told to "Stay your ass in your lan alright, or you get f**ked up." If it's reasonable to take that as a threat (and it sounds like it is), then it appears that you violated the policy even if you didn't intend to make any threats yourself. Of course, that's just my take on it, but I think that you'd have a hard time convincing a court that you were wrongfully terminated given these facts.
On the other hand, you also indicated that you were the victim of discrimination based upon your race. That is certainly illegal. If the EEOC does not do anything for you, then you should request a right to sue letter. Once you have that letter, then you can retain a local attorney to sue the employer. In order to prove the racial discrimination, you will need to show that non-black employees in the same circumstances are treated differently. For example, you mentioned your pay as an issue. You will need to show that non-black employees with the same duties and same experience earn more. That is the best way to prove discrimination, unless you have a smoking gun ... e.g., an email from management stating something like "don't give black people raises."
In sum, it sounds like may have recourse at least regarding the discrimination. I think you'll be fighting an uphill battle regarding the termination, however, since the voicemail could be construed as threatening (though again, that's just my take on it ... you certainly have the right to sue the employer and try to argue that your voicemail did not violate the policy).
Does that answer your question? Please let me know if you need clarification, as I am happy to continue helping you until you are satisfied.