An SR22 is not a form of insurance, even though it is typically purchased from an auto insurance company and a requirement for driving a vehicle under certain circumstances. The SR22 is known as a Financial Responsibility Statement, and is usually required under serious traffic offenses such as a DUI or even reckless driving. When it is required, you must purchase the SR22 along with insurance for your car, and the SR22 must remain in effect throughout the required period of time.
In some states, you may be required to have an SR22 if you were not insured and involved in an accident as well. In this case, the SR22 serves as a penalty for displaying contempt of the auto insurance laws of your state, and may be required for up to 5 years, even if you are not driving a vehicle at all during a portion of that period. In most states, the same is true for car insurance, too. If the car is registered, it must be insured at the state's minimum insurance requirements or you may forfeit your driver license or car tags and registration.
Your SR22 filing may be included in your car insurance premiums, but a closer examination of an insurance bill will reveal that the SR22 is added into the cost, not included as part of the original policy. In some cases, the SR22 requirement is also an automatic increase in your insurance rates, especially in cases where DUI or driving without proper insurance are concerned.