when I make an outgoing call, my cheek is touching the screen while I am talking on the phone, and it makes the phone do things like, go on the internet, go into my calendar, whatever my cheek is touching on the screen at the time. I can't seem to lock it after dialing a number, so when I talk, I can't help but touch the screen with my cheek. How can I lock it after I dial so my cheek doesn't do things to my phone while I talk on the phone?