Corp cal is here to stay unless you're hacking your phone as others have said. Also please note, if you remove corp cal and then later try to apply the OEM update that may come, it will probably fail (I believe the update process validates certain things and if it doesn't find that application it might bag). All that said, if you have root access, you can indeed mount the system partition and do something like mv CorpCal.apk CorpCal.apk.bak (im not sure of the real file name). Then if you ever want to go back to the OEM update route, simply move it back into its original filename. I do not sugest messing with system file partitions unless you know what you are doing AND of course have backups, this is merely an explanation of how to do it.