My simpliest answer would be to make arrangements to go out of your house that way you won't have the access. Obviously if your phone has internet useage then what you can do is make sure you have a plan for an activity that your about to do. I have limited my time on here and on the internet in general by watching tv/dvds, reading, socialising etc etc!!

Maybe make a list of things you can do?

It doesn't always work and there will be days you want to sit on here all the time but hey your allowed that!!