For sole proprietors, the Solo 401(k) offers the same plan options, contribution limits and flexibility that are available in company 401(k) plans. As a result, single owner businesses are able to put away more money for retirement in a shorter amount of time using a combination of salary deferral and profit sharing contributions. Opening a Solo 401(k) with Millennium Trust offers the added benefit of being able to invest retirement funds in a broad range of investments, including traditional and alternative investments.