kdeconnect-handler has some special cases to improve strings when sending tel: URIs. The same should be done for sms: URIs.

Instead of showing
"Device to send sms:12345 to"
it should show something like
"Device to send a SMS with"

Relevant code is at https://invent.kde.org/kde/kdeconnect-kde/blob/master/urlhandler/kdeconnect-handler.cpp

You can trigger the dialog like this:

kdeconnect-handler sms:/12345