Sending a gratis SMS to Belgian GSM subscribers impossible? No SMS-email gateways? SMS 2.0 (RCS) only for Google patrons… - Brussels - Fedia
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Mobile carriers in [many countries](http://www.arkaye.com/IntlEmail-SMSGateways60809.htm) provide a free email→SMS gateway service, so if you have no SMS capability or credit, or you are outside the country you can still get an SMS to someone using just email....

RCS seems to be replacing email-SMS gateways. RCS is supposedly an open standard, but apparently if you do not have Android 8.1 or newer, you cannot use RCS to send an SMS in Belgium.

In principle, iiuc, you should be able to use a desktop app or browser to send an RCS msg. But for some reason it’s a shitshow.