So I Won't Have To Remember

Iphone call log is located under /User/Library/CallHistory in a file named call_history.db. This file is a SQLite database. There is a table named call which holds the log.

There is another table in this database named "_SqliteDatabaseProperties". This table store call log properties in key => value format. One of the property here is call_history_limit which is set to 100 by default. Change that number to something like 500 to store last 500 entries.

You could use a SQLite Manager (firefox add-on) to do this or write a quick java program.