I don't believe that to be entirely true. My inReach number is always the same I've texted my wife and myself and others and my number is always the same.Forgot to answer the question, when the receiving party gets a text for another phone number not yours, multiple text get different numbers not your number. To answer a text the caller has to use that number, not your cell number.
Someone else can't text you until you text them first.
If you plan on exchanging texts, start the text with InReach. Then they came answer your text at any time.