I've recently got my parents a TVPad but they don't have the internet

Looking at signing them up to Slingshot's $81 Better Network plan however on their website it says I have to sign up for a minimum of 12 months. Which is fairly common but there's no freebie to lock one in - i.e. no modem, no free two months or anything.

I do get a free wireless modem plus another 200GB if I sign up for their $69 20GB plan

Does anyone know if I sign my folks up for that whether I can upgrade plans at any time (i.e. to the $81 plan after say 2 months???)

Also - is their refer a friend offer still on?