This is more of a tip more then anything (not really a find, but a small feature that a lot of people don't know exists). I remember that the game goes over it with you at some point, but it is useful for those that are sick of doing shit for friends and stuff.

You go into options on your cell phone, and there is an option to put it on sleep. If you do, you can essentially pause the story progress and free roam without people calling you ever 5 minutes.

Yep, just like it says in the first mission (tutorial). You can also use the simple native trainer to disable the phone all together.