Inside sales refers to the activity of reaching out to prospects remotely, using the phone in order to communicate and educate them enough that they become a qualified sales opportunity. Once the prospect is qualified (SQL), the job of inside sales is to hand them off to outside sales.
At a certain point in the growth of your business, trying to generate leads for yourself is no longer the most efficient option, and outsourcing B2B lead generation becomes the most effective way to get a good ROI.
Complex B2B sales require making a quality connection with a key decision maker. That quality connection must establish trust and be solid enough to carry the business relationship through a long and complex sales cycle. It is why cold calling is an extremely effective method for B2B lead generation.