Deported US citizen back to Jamaica, can he return eventually??

I assume that your friend is not a US citizen unless part of his deportation process involved taking back US citizenship because he illegally obtained it. Otherwise US citizens are not deportable. If there was indeed such a mistake, it could be redressed by presenting proof of US citizenship to the US consulate or embassy, Department of Homeland Security, or suing in a federal court. If he is not a citizen, his ability to return to the States would depend upon what type of crime he served time for and what his reason would be to return to the States. That decision would be in the hands of a US consular officer and Customs and Border Protection (CBP). If he is able to come, the U.S. government may require a waiver of inadmissibility before giving him either nonimmigrant or immigrant visa. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.

If he was deported because his conviction qualified as an "aggravated felony" then he is barred for life from returning to the US.  The only chance of return would be to challenge his criminal conviction collaterally.  This requires hiring a lawyer that specializes in post-conviction relief in the jursidction in which he was convicted.  Even if the conviction is overturned, there is no guarantee the result will allow him to return, but it is the only hope such individuals have.