Now that smartphones are so connectible (Bluetooth, Wi-Fi,, S-Beam), I'd like to get some opinions on security options beyond just malware protection. I imagine that they can be infected with trojans, worms, and viruses the same way as PCs are (because they practically ARE PCs now). So I ask: What do you use (or recommend)?
If you are talking about an iPhone, there really isn't anything to install. Whether or not an iPhone is truly vulnerable or not (an entirely other topic/debate), the reality is that there are no "direct"/"automatic" malware/anti-virus programs/utilities available through the App Store...at least that I am aware of. There are some "manual" anti-virus/malware apps that you can use to manually scan attachments from emails, but they are more for the purposes of catching something that you might later forward to someone else using a computer or even if you transfer that file to your own computer. Thus, even if you believe that iPhones can get hacked/infected/etc, there is nothing really out there to install. As a result, the main security related things for an iPhone is that it you dramatically weaken the defenses of an iPhone if you jailbreak it (there may be anti-virus/malware programs available for jailbroken iPhones)...beyond that it is mainly an issue of physical security. Use some sort of "find you phone" service to help find it if you lose it, but more importantly to be able to lock and wipe it. Secure it with a passcode.
For Android, there are a number of anti-virus/malware type programs out there. When I had an Evo 3G, I used Lookout Security. It has been almost two years since that time, however, so I don't know how good it still might be (malware was a relatively minor issue back then...it is has become more of an issue these days). There are certainly other choices (some from the "big names" in the computer security world), but since I have not used any of them, I cannot really comment. Someone else might be able to offer an opinion.
As for Windows Mobile phones, I have no direct experience with them, so I cannot really help there. Same with Blackberry.