Telemarketing service plays a big role when it comes to attaining good leads at the highest level, phone calls are one part of the process, and when I say phone call I mean real humans reaching out to clients and not a bot or any automation of some sort.
The quality curve has also been tackled in this video like "the number of leads doesn't go up unless your budget goes up in most prices" as well as tips on when is the best time and type of day to make a call to clients.
To know more about what to expect with conversions, watch this video https://www.youtube.com/watch?v=9j7N87Rhuhw