i found this recently http://seattletimes.nwsource.com/htm...llvirus26.html
this article only shows existance of cellphone viruses no trojan horse no keyloggers..........
different cellphone run on different OS so hackers have to design different codes for different cellphones also major mobile companies like nokia are planning antivirus protection for there new java enabled handsets.
i searched a lot on google on the topic but there is no information on how hackers are developing cellphone viruses

still in its early stages cellphone hacking may become a major security issue for cellphone holders specially those who use cellphone for banking,ticket reservation etc.....

Cabir is a network worm that infects phones running the Symbian mobile phone operating system by Symbian. No infections have been reported. Cabir may be a proof of concept worm...

Cabir spreads between mobile phones using a specially formatted Symbian operating system distribution (or SIS) file disguised as a security management utility. When the infected file is launched, the mobile phone's screen displays the word "Caribe" and the worm modifies the Symbian operating system so that Cabir is started each time the phone is turned on.

Once it has infected a mobile phone, Cabir scans for other phones using Bluetooth wireless technology, then sends a copy of itself to the first vulnerable phone it finds, Kaspersky said.
references:
http://news.com.com/Skulls+program+c...tag=st.ref.goo
http://www.pcworld.com/news/article/0,aid,116508,00.asp
http://www.news24.com/News24/Technol...543214,00.html

http://news.com.com/Skulls+program+c...tag=st.ref.goo