Every once in awhile I come across some really neat freeware that I think you folks could benefit from.

PhoneLog is a freeware app from InfinityBall (click for more screenshots) that simply logs your call log directly to your calendar app.

This is all done instantly in the background with no noticeable performance issues--it just works seamlessly and efficiently which is the best kind of WM app.  After a call, in your calendar it will say "Talked to " with the start/end times and call duration.  The info shows up as a simple entry in your cal and you can even assign it a custom category.  

The app does require .NET compact framework 3.5 and has many configuration options such as log missed calls, all calls, run on startup and even log your text messages (!)  Very cool stuff.  Get it here.