There are many ways to do lead generation. Some are very ethical and some are illegal. What type you choose depends on your goals and strategies.
For example, if you buy lists of emails an upload them to a system that spams everyone you could be breaking the law.
If you are sending automated phone messages - you may be doing it as well. Especially if the number is on the do not call list.
But then there are techniques for less lazy people such as constructing sites that have useful information and attract buyers to them. This is called Inbound Marketing, and while it is not instant, it is very effective.