I notice that I don't need my 4G to be on all the time, I only need 4G when I'm actively web browsing. Is there an app that keeps the phone in 3G during idle use, but switches to 4G whenever I unlock my phone or when I bring up my web browser? I do not want to manually toggle 3G versus 4G. I would like an app that knows when to switch between 3G and 4G based on phone lock status or web browser usage (or better yet, bandwidth usage). Any guide/direction would be appreciated!