Can a Company, who currently sponsors a SIMPLE-IRA Plan, terminate the SIMPLE Plan and put in a 401(K) in the same calendar year. (I am pretty sure you cannot put in a SIMPLE in a calendar year that you have a 401(a) type plan - BUT is the reverse also not allowed)

No. A SIMPLE IRA cannot be maintained in any year that the employer maintained any other plan. It doesn’t matter which was done first. Furthermore, a SIMPLE IRA may not be terminated in mid year, unless the employer has an unavoidable circumstance that would result in termination of the plan, such as terminating the business. The fact that the employer wants to establish another plan, means that he/she has no grounds for terminating the SIMPLE plan

Absent state law to the contrary, a SIMPLE can be terminated at any time without further obligation. It can also be amended at any time (effective as of the beginning of the year) if the amendment is not inconsistant with the annual Notification to employees. If terminated mid-year (OTHER than by the adoption of and accrual of benefits in another plan), it is still possible that the SIMPLE remains valid for the tax year. All contributions must be made prior to termination.