You don't need one.
read the full answer from here: http://discussions.nokia.com/t5/Pool-of-Knowledge/
Is my Nokia Series 40 device at risk from viruses?
Absolutely not. Series 40 (also known as S40) devices can only run Java applications in .jad or .jar formats, these can only be installed and run at your own instigation, no program can get into your Series 40 phone without your knowledge, and it would not be possible for them to make changes to your device operating system.