Last I heard, there were less viruses for winmo (or mobile devices period) than you could count on one hand. In fact, the only virus I've ever heard of is the "Cabir" virus, which was specifically designed as a proof-of-concept, and
AFAIK never entered the mainstream. There are rumors of MMS/bluetooth transmissible viruses, but again
AFAIK, they haven't gotten into the mainstream either. In fact, as I understand, the carrier checks for malicious content over the air. Analysts have determined that the threat of point-to-point viruses is very little. Rather, it is anticipated that when viruses become a serious threat, they will be in the form of auto-distribution type viruses (IE: something that would send itself to everyone in your contacts list). In any case, I would suggest pocketing your money, and forgo the virus software. If you're that concerned about them, all you need to do is be careful about the MMS you open, and don't leave your bluetooth in discoverable mode.