1.) Yes and no on the weekend from what I saw. You still get up really early on saturday, but nothing on sunday. If I'm not mistaken there is also no classes on the weekends.
Usually Sunday's do not have duties as a plebe, but you may still be busy if you are on a club team, etc. It's also the best time to get ahead of your homework. DS basically does not rest on Sunday until he has his homework & projects done at least thru Wed.
Saturdays vary. There is a schedule (A weekends, B Weekends, etc) that make the difference. From memory there are three different saturdays with one of them being free.
On one of them you will be busy drilling in the morning unless at corps squad club team competition or practice.
You will be expected to attend home football games unless off at competition or practice.
Some Sat's will have parades, which you will need to participate in unless excused. (But may still be pressganged into attending).
SAMI is another Sat AM killer.
And if you fail it, you get to retake it another Saturday.
Sat afternoons normally free unless there is a home game or other mandantory spirit event.
Think I read somewhere about 1/3 of your Saturday's will be free.
My understanding on the landline is that it is deducted from pay, so there is no reason not to use it. And most barracks have poor cell coverage. It does come with unlimited long distance. I want to say it's a $20 charge, but you never see it as it's deducted prior. All you see is the $225 per month paycheck leftover. Enough for pizzas on the weekend and other small expenses.
Based on observation, most FB activity takes place during enforced study period (each weeknight) or occasionally in class gaps during the day. You'll also have "drops" when a class does not meet occasionally.