How to Check Free-Busy information on your Windows Mobile Device (ver. 5.x, 6.x)
When Windows Mobile 5 was released it was released without the ability to do GAL lookup. To deal with this a add-on was developed from the product team that allowed you to do both GAL Lookup and check Free-Busy. Well in Windows Mobile 5.0 GAL lookup was added but we still don't have Free-Busy look up. Well since the tool still exists you can download it and use it to check Free-Busy information.
https://www.microsoft.com/windowsmobile/global/default.mspx
The Microsoft Global Contact Access Application uses the OWA Web Service to check free busy information. It's important to note that the OWA Web Service is not the same as the Activesync Web Service (both can be seen on the IIS server under the Default Web Site) which is used to sync Calendar, Contacts, Tasks and Mail.
This Works with Exchange 2003 and Windows Mobile 5.x and 6.x - I have yet to test it with Exchange 2007.