Hi lip,
The rule is a little different from how you word it...you cannot maintain a SIMPLE while you maintain another retirement plan...except where exceptions apply

....So, if the SIMPLE IRA is being maintained for the year, the employer cannot maintain another retirement plan. If both plans are maintained, the SIMPLE IRA contributions for the year are disqualified. If no contributions are made to the SIMPLE for the year, then the employer can maintain the other plan for the year.