If you buy an internet modem from Walmart or online are their monthly fees? ?

You pay monthly fees to your internet Service provider for your Internet Connection NOT the Modem.

No fee. Just what ever the ISP charges for internet.

HOWEVER,. the modem must be one that is on the approved list for the ISP. THEY maintain the code that is on it and the permissions. Therefor, the modem must be one their system understands.

Nope. You only bought the modem. Monthly fees are collected by the ISP (Internet Service Provider). BTW, if you subscribe to an ISP, they supply you with a free modem and router or whatever is needed to connect your computer to the internet. They will also setup everything for free.

You pay full price and modem is yours.You pay monthly fees to internet provider for modem because they do not sell it to you but rent it.When you cancel the service you have to return modem to the company.