On the hardware keyboard, the "l" key popped up the calendar app every time I pressed it when texting. Using the screen keyboard, it didn't do this.
It just started happening out of nowhere, and I noticed in the recent search terms on this site someone else searched for the same issue.
I did *228 to reprogram the phone and it still launched calendar with the "l" key.
Finally, I reset the phone by popping the battery out and putting it in after a few seconds. This fixed the problem.
Just an FYI for anyone else out there who discovers this strange Easter Egg.