I understand your aversion to trying it and getting charged - but like iMessage, RCS messages aren’t sent by T-Mobile* (which is probably why you can’t find anything on how much it costs).
*Unless you send it over mobile data
Both RCS and iMessage work like Whatsapp or any other “data” driving application where it’s WiFi/Mobile data to send the message. SMS costs you money because it’s sent over cellular only.
However, an easy way to test without getting charged would be to enable airplane mode and then only turn on WiFi. Once you’ve done that, try sending an RCS message over Google messages.
Remember, RCS only works when the recipient also has Google Messages* and you’ll need to have WiFi calling enabled.
I understand your aversion to trying it and getting charged - but like iMessage, RCS messages aren’t sent by T-Mobile* (which is probably why you can’t find anything on how much it costs).
Both RCS and iMessage work like Whatsapp or any other “data” driving application where it’s WiFi/Mobile data to send the message. SMS costs you money because it’s sent over cellular only.
However, an easy way to test without getting charged would be to enable airplane mode and then only turn on WiFi. Once you’ve done that, try sending an RCS message over Google messages.
Remember, RCS only works when the recipient also has Google Messages* and you’ll need to have WiFi calling enabled.
Technically, it looks like the default messaging app might work for T-Mobile users.