I am releasing a new utility written for Android which I use for logging when I call people and when they call me. Others can use it to track calls for billing/invoicing purposes. When it runs in the background, you can select it and it will write an entry in your chosen calendar.
The Application can be downloaded from here for the small sum of 50p. I hope you find it useful, and worth it. I use it to log when people call me and when I call them, all part of the Pastoral Cycle.