Knowing which numbers are capable of receiving SMS and which aren't has some value.
Especially in a world of number portability where you can't just say "oh, that's an old number, it must be POTS".
But I guess, here, if a number is from your contact list, it may still be POTS.
But at least you have higher assurance that it's an active user. If you wardial one day, you quickly find out how many numbers never lead to a human for various reasons. In theory, some of these are trap numbers and quickly flag the caller as suspicious, but I doubt it.
"Knowing which numbers are capable of receiving SMS and which aren't has some value."
This isn't difficult - I wrote a shell script named "lookup" that will give me background info for any phone number I feed it and tell me what kind of number it is, what carrier it is, who it belongs to, etc.:
The Local Routing Number provides this value in the USA, and multiple carriers (eg:Twilio) offer daily deactivation reports from the cellular carriers so you can tell which numbers are unroutable.
Especially in a world of number portability where you can't just say "oh, that's an old number, it must be POTS".
But I guess, here, if a number is from your contact list, it may still be POTS.
But at least you have higher assurance that it's an active user. If you wardial one day, you quickly find out how many numbers never lead to a human for various reasons. In theory, some of these are trap numbers and quickly flag the caller as suspicious, but I doubt it.