Test messages being sent to landline contacts rather than their mobile phone
I have an iPhone 13 Pro Max.
Sometimes, when I try to text someone, the phone choose their "home" or "work" phone instead of the one marked "mobile".
I send a text message, assuming its been sent. I don't hear back from the person, and then I check the message I see it tried to go to "home"!
When we make contacts, we are forced to go to some trouble, including labelling phone numbers as "mobile, iPhone, home, work" etc.
Text messages should ONLY go to a number that's labelled as "mobile" or "iPhone". That would solve the problem.