Why a purchased number list costs you money
Buying a list looks like a quick start. In practice it is the most expensive way to begin.
It is not allowed
For commercial messages you need consent, and consent cannot be sold along with a file. In the event of a complaint you must be able to show when and for what somebody consented. With a purchased list that is by definition impossible.
It does not work
Such lists contain many dead numbers, which you pay for regardless. And the people who are actually there are not expecting you — that produces opt-outs and complaints rather than sales.
It damages your sender
Complaints attach to your sender name. One send to a bad list can affect your delivery for months, including messages to your real customers.
What does work
Ask for the number at the moments when you are already in contact: during an order, an appointment, at the till. Say what people will get and how often. Such a list grows more slowly and returns far more.