The sales thing is super important but the channels and investment really depend on the type of business. B2C won't scale with phone calls you need marketing organization.
Scaling sales is a very different thing from getting sales, and I'd argue you won't know how to scale until you find a channel that works but is not cost effective. Otherwise you're essentially shooting blind, but at scale, which doesn't hit much but uses a lot of ammo.
I'm thinking more from the low-touch, low-margin perspective. If you are trying to make money with ads, calling 70 people to get 70 ad views is a terrible ROI no matter how persuasive you are. If you're selling a subscription SaaS product and expecting a lifetime value in the thousands per customer, then cold calling is a pretty decent way to bootstrap.