I'm trying to track down the link, but most mobile AV apps are completely useless in protecting against the threats we see out there these days. They are effective at causing an additional drain on your battery and a performance hit, though. The most common attack vector we see is malware infecting phones through malicious apps downloaded from the Market. Instead of using AV on your phone, I strongly suggest you simply stop and think before you install any app, read and understand the permissions the app is requesting, and then make a reasonable risk-based decision on if you trust the author of that app not to abuse those privileges (e.g. it's probably ok to allow Google as the author of Google Latitude to access your contacts, but it's probably not ok to allow Johnny Sticky Fingers of Big Tits HD Remix Live Wallpaper that same access).