...with AE Button Plus.
This little application allows you to assign custom actions to any of the hardware buttons on your Windows Mobile Pocket PC or Smartphone device. An 'action' being a single, double or even triple key sequence. There are over 40 built in shortcuts, but the software is also customisable to allow specific 'macro' functionality.
Read more about the product on the Smartphone Thoughts web site:
http://software.smartphonethoughts.com/product.asp?id=14573