If you use the internet most of the time then you shall sign up for the monthly price, it will be cheaper in the long run.
The one month trial is free unless the there is a contract where you must cancel after the month so you will not get charged. Just make sure you read the contract rules/
You can undo the monthly thing by logging into your account if you creat one and just change or switch back to what ever you want.
You have any questions go to their website and call them up they will be happy to help you