By default, Siri will read your text messages back to you before sending them, but you can turn this off.
You can invite someone to Signal using the "Invite Friends" menu in the app, which will send a text message or email.
If you have an iPhone 14 (or newer) or a Google Pixel 9, you can send texts via SOS Mode. My title is Senior Features Writer, which is a license to write about absolutely anything if I can connect it ...