I didn't know these until last week, god knows why as one of them is pretty obvious:
1. To lock your Nokia 3650 keypad, from the main screen click the left selection key and then immediately after click the asterisk key. It doesn't matter what you have assigned to the selection key (I have Messages there), if you click the asterisk immediately after, it'll lock the keypad. It's basically the exact same process as unlocking the keypad, except that it's not nearly as obvious. (I've had my phone since February and this is the first I've known of this.)
2. To make sure that no memory-resident programs start when you reboot your phone, hold down the pencil key when you turn the phone on. I don't have anything running on my phone that this affects, but the idea is that you can stop some of those apps - say Handy Day or something like it - that starts up automatically when you restart the phone.
I've been meaning to post this for over a week and there's more in the pipeline... I just need to remember...
Hey! Any more tips like this for S60 phones that you know of?