From [0], it seems that RCS can use the cellular signal instead of LTE or 5G:

> In cases where RCS is able to operate over cellular networks without data, it supports messaging as well as file transfer, enriched calling, and more.

[0]: https://en.wikipedia.org/wiki/Rich_Communication_Services

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wolvoleo 2 hours ago | parent [-]

In LTE and 5G there exists no cellular signal without data. That was a 2G/3G thing. Since 4G everything is data. The separate sms and voice services are gone. And 3G is rapidly being deprecated.

	▲	MrDrMcCoy 5 minutes ago \| parent [-]
		That's not quite true. VoLTE was an optional part of 4G in the beginning. I had one of the gaming ASUS phones that shipped with 4G, but no VoLTE. 6 months after getting it, the US phone carriers conspired to make VoLTE mandatory for connecting to their towers, effectively bricking my device. ASUS never issued the firmware update that would have enabled the feature in the modem, which had the capability, and the community hack to enable it never worked for me.