Q: Which OS is safest for Wi-Fi: Apple's iOS, Google's Android, Microsoft's Windows Mobile, or other?
A: I get this question a lot. The simple answer is that there is no truly secure mobile OS today.
All of today's mobile platforms promise some level of device protection in the event of device loss. The common features include device encryption, remote wiping, or even remote bricking to completely disable the device. The problem is that these security features must be managed by corporate IT. And remote wiping and bricking depend on the device owner noticing the device is missing and promptly informing IT of the loss.
Few users are willing to contact IT the moment they notice their iPhone or Droid is missing, opting to spend hours looking around or calling home, work, restaurants, airlines, etc. Add up that time. That's the amount of time an attacker has to turn off the phone, which will stop it from receiving the self-destruct signal. A dedicated attacker does this, and then only powers on the device in an isolated area where IT can't remotely destroy it.
As for device encryption, there's little published data from any OS or device manufacturer on how this works. So you're taking Apple, Google, and Microsoft at their word when they promise encryption. That might suffice in some IT shops, but I only consider encryption reliable when documented and proven by tests.