The Beselo worm, as F-Secure has dubbed it, is actually an SIS application installation file in the guise of media files named beauty.jpg, sex.mp3, and love.rm. And just like the early Commwarrior worm that targets Symbian phones, Beselo attempts to spread through MMS and Bluetooth.
Fortunately, and unlike nasty buffer-overflow style worms that don't require any user input, this worm requires users to interact in order to spread. And so for careful users it's not a problem. As hard as it may be to do so, just reject beauty, love, and sex by replying "no."
The time to be concerned with mobile malware will come, but it's not today. A little common sense goes a long way at avoiding social engineering tactics. Nonetheless, I still leave the Bluetooth, Edge, and Wi-fi connections on my T-Mobile Sidekick off -- unless I'm using them at that very moment. Unless you're holding very sensitive data, or are of the especially paranoid type, mobile antivirus products are unnecessary.
My bet is that the first, widespread malware attack will be aimed at the iPhone, and spread through a (or what appears to be a) media file. Let's all hope Apple gets the SDK right when it comes out next month.