PhoneLog is a freeware for Windows Mobile users, which could keep records of your incoming, outgoing or missed calls in logs. It attached the log files with calendar application.
Runs in background and works efficiently. Make log files with call start time, end time and duration. It doesn’t only create log for calls but also for text messages.

PhoneLog works with .NET compact framework 3.5. Try PhoneLog and take advantage of it.

Download .NET Compact Framework 3.5
Download PhoneLog