I think it would be strange if Romans 10:9-10 were referring to the salvation of our soul because that would mean that we became "righteous" when we believed, but we weren't "saved" until we call upon the Lord. I don't think it is possible to separate the righteousness and salvation of the soul. Also, if Paul is referring to the individual salvation of the soul, it would be strange that he did not mention it in chapters 3-5 of Romans where he was dealing with salvation from sin. And again when Paul mentions the gospel in Rom. 10:16 it is said that you obey it by believing it, not by confessing.