It doesn't have to be notarized. See here for details:
<a href="
http://www.irs.gov/Individuals/International-Taxpayers/Nonresident-Spouse-Treated-as-a-Resident" rel="nofollow" target="_blank">
http://www.irs.gov/Individuals/International-Taxpayers/Nonresident-Spouse-Treated-as-a-Resident</a>
How to Make the Choice
Attach a statement, signed by both spouses, to your joint return for the first tax year for which the choice applies. It should contain the following information:
A declaration that one spouse was a nonresident alien and the other spouse a U.S. citizen or resident alien on the last day of your tax year, and that you choose to be treated as U.S. residents for the entire tax year
The name, address, and identification number of each spouse. (If one spouse died, include the name and address of the person making the choice for the deceased spouse.)
