Trend Micro Mobile Security 2.0 provides handset security including antivirus and SMS spam detection for mobile phones and PDA devices.  Service providers, enterprises with mission critical mobile infrastructures, as well as consumers requiring security software for portable devices may use the solution.

Trend have just released a beta that supports Windows Mobile 5.0 for their solution. 

You can get more details:

https://www.trendbeta.com/index.php?get=37