There is a short message chat room in oppo mobile phone. Does it cost money? About how much?

Hello, chat rooms in mobile phones are basically available in domestic mobile phones. Chat is a bit like QQ, where both parties' information will be displayed, but the difference is that QQ chat is connected by mobile phone traffic, and the cost is low, while chat room is connected by mobile phone SMS. Every message (70 words) you send is charged according to a short message, which is essentially no different from a short message, but once the chat room exits, the message you send does not exist, unlike a short message.