You may not have noticed it, but the newer mobile phones have enhanced security features to guard against malware, viruses and worms. The newer phones based on Nokia Series 60 Third Edition (e.g. Nokia N73) and UIQ 3.0 (e.g. Sony Ericsson M600i) support the Symbian Signed security feature. All Symbian applications developed for these phones will have to be certified and digitally signed before they can be installed in these phones.
What does Symbian Signed mean to you?
Have you been affected by worms infecting your phone through Bluetooth or MMS? (Here's an example.) With the newer phones it's harder to get infected by the worms because the worm software would not be certified and digitally signed. Without the digital signature, the phones would refuse to allow the worm software to be installed.
What does Symbian Signed mean to developers?
Unfortunately developers will have a tougher time testing and deploying their Symbian mobile applications on Symbian phones. Symbian offers the most power and flexibility for mobile applications, even more than J2ME, that's why some applications are developed using the Symbian platform.
To test a Symbian application on a single handset, the developer needs to apply for a digital certificate (which costs money) and use Symbian's online service to sign the application digitally. During signing, the developer needs to provide the IMEI of the handset to be tested. Once the digital signature is obtained, the application may be installed on that handset. The developer repeats the process for each additional handset to be tested. See how cumbersome the testing becomes?
To deploy the finished application on a large number of handsets, the developer needs to submit the application to a third-party testing facility, appointed by Symbian, to get certification. Only after the application has been certified can it be signed for general release, to be installed on any compatible handset.
So Symbian Signed definitely helps to protect your phone from malware, viruses and worms. However, it does make life more difficult for Symbian developers everywhere, like me.