Our QA department has just released a public beta of Panda MobileSecure for Smartphones (here). Even though we don't consider this as a high threat arena for malicious code yet, it doesn't hurt to be prepared in case the situation changes in the future.
It scans in real-time for viruses and other threats in files, email and multimedia messages. It also includes a wireless filter that detects malware being transmited via Bluetooth or IrDA, as well as an on-demand scanner.
Currently supports Symbian OS 7.0, 7.0S, 8.0A, and 8.1. You'll need 500kb of free space. Nokia's N90 is not supported. You can download the installation package from here and configure the signature updates with username "CCF2276EGU" and password "A6D2DGVW" (Note: case sensitive. Use without quotes).