Can I use my own hotspot on my Verizon iPhone 4 as my own personal Wi-Fi?

Me and my mother just got iPhone 4's from Verizon. I see that my phone has a personal hotspot, could I use that to my advantage because verizon doesn't have unlimited Internet. Also why does it say I can't use my mothers hotspot when she turns hers on? So many questions!

You may see the option to turn on a hotspot, but usually having a hotspot costs extra. $35+ extra. Not sure why you can't use your mothers.

You need her network password