The quick answer is YES investing time making calls works - if done in the right way at the right time by the right person for the right prospect.
The human approach is an absolute must. Having a voice helps to differentiate you from someone else and better conveys your individual personality. So if you can't get an opportunity to meet prospects face to face at shows or other physical networking events, etc, sparking up a direct conversation with a decision maker via telemarketing is an efficient and less costly way to introduce your company.
Digital methods via email and social media are good tech alternatives, but if you can initially connect with someone in person or via a call, there are some great advantages:
To get the same response via digital methods you'd have to hope that your prospect is willing to take the time to type back a lengthy informative response that hopefully includes answers to any research and discovery questions you may have or take part in some email ping-pong.
Usually it's far more efficient to speak than type but at times it may be a blend of communication methods required. Really it's finding the channel/s that a prospect is happy to engage with and working out which method at any particular time is best for the person your trying to reach.
A rejection is not usually personal as most people will only really want to speak when they have a need for whatever it is your ringing about - so timing is important. Not everyone likes to prospect over the phone so it's best to have someone who is happy and able to do that type of work.
I've spoken to lots of decision makers who are open to calls from potentially right fit agencies as it saves them the time and effort researching into it themselves. Of course some prospects are email only so you must hone your writing skills - especially to a typical busy decision maker's bombarded inbox.
So as well as getting yourself seen, make yourself heard.
Have a Happy and Prosperous 2020.