Both sim-cards book money for Internet?

I ´m going to take using of the option to use two simcards.
So some questions are taking my thinking.
First I would like to know if both cards ´d be active at the same time.
Then there is the question what happened if I ´d use two simcards, which allowed me to use mobile Internet and I did it. Would both simcards take my money in a situation like this?
Is there any application I need to avoid that both simcards take money for the one Internet I ´d use?
Another question standing on my way is when mobile Internet become booke.
When I get an social media message?
When I get an E-mail?

Thank u for your attention for my little questions :smile:

Only one simcard can get a 3G connection.
Both simcards can be active at the same time, but having said that, if you want to make a call, send a message, use internet you have to choose which simcard you will use.
So you can’t be charged on both simcards for the same action.
It depends on your own configuration when you get an e-mail, social media message.
You can able of disable roaming.