Skulls.AF is a malicious SIS file trojan that will replace the system applications with non-functional versions, so that all but the phone functionality will be disabled. If Skulls is installed it will cause all application icons to be replaced with pictures of skulls, and the icons don't refer to the actual applications any more so none of the Phone System applications will be able to start.
Use F-Skulls to allow for installation of F-Secure Mobile Anti-Virus
Install F-Secure Mobile Anti-Virus
CAUTION! this method will remove all data on the device including calendar and phone numbers:
Prevent future infections with F-Secure Mobile Security
Skulls.AF is a SIS file that installs critical System ROM binaries and Cabir.F and Cabir.G worms onto the C: drive. The System ROM files are installed with exactly the same names and locations as in the ROM drive.
The Symbian operating system has a feature which causes any file that is in the C: drive to replace the file in the ROM drive with an identical name and location.
Replaces built in applications with non-functional ones and installs Cabir.F and Cabir.G worms.
F-Secure Mobile Anti-Virus for Symbian detects this malware starting from the update build number 11.