Sending emoji via SMS with UTF-8 (rather than UTF-16)?
Sadly this is a limitation in the SMS protocol.

The "ascii" charset is not the normal we are used to in the computer world, instead it is a 7bit (or GSM 03.38 https://en.wikipedia.org/wiki/GSM_03.38) and very limited.

If one single character is used outside of this 7 bit charset, it is switched to UCS2 (See more information about UCS2 not exactly being UTF-16 here https://en.wikipedia.org/wiki/UTF-16).

With 7 bit, each character takes 7 bits (doh), and with UCS2 each character takes 16 bits.

While coding some SMPP (the SMS protocol) integrations, I've seen sporadic support for other charsets, but I do not think this is at all adopted in the wild.