Is it free to send Tianjin Mobile family number text messages casually?

It seems...

Tianjin Mobile's newly launched M-Zone music package "Family SMS Package" does not offer discounts on phone calls, but only offers discounts on sending text messages.

You can set up two Tianjin Mobile numbers as relatives and friends, and there is no charge for sending text messages to these two numbers. The business fee for this function is 2 yuan/month