Line type
Whether a number is a mobile, a landline, or a VOIP line.
Line type drives what you can legally and practically do with a number. Text messages only reach mobiles. Some jurisdictions treat automated calls to mobiles more strictly than calls to landlines. VOIP numbers are cheap to obtain in bulk, which makes them a common signal in signup fraud.
In most countries the numbering plan encodes it: a prefix range is designated mobile or fixed, so the classification comes straight from the number. In the North American plan it does not, because mobile and landline share the same ranges, which is why a US line type needs carrier data rather than a prefix rule.
A line type result is not permission to contact anyone. Consent is a separate question, governed by the TCPA and equivalent laws.