Cold calling is one of the oldest tricks in the sales book but it's also an important tool in the Solution Validation kit. Talking to users is the best way to get feedback on your proposed solution so if you have the benefit of direct access to potential users by phone then it's important to take advantage of the wealth of information that that access could represent. Prepare yourself with both your pitch points and a short interview script that covers the most important information you need and get ready for the inevitable hang ups that will happen. Though sales calls can be a tough business every successful conversation will result in great insights that you wouldn't otherwise have.
Sales calls are best pursued when you're into Solution Validation and you have a clear idea of your product or service offering.
Sales calls are a great means of contacting users that belong to a specific target industry or business. Catching them at their desk when they are facing the problem you're trying to solve could also provide insights that otherwise could go unnoticed or unmentioned by the user.
A phone, a list of numbers, your product details and pitch and a few questions related to your research area. If you're looking for leads to call you can start with LinkedIn to identify appropriate contacts or companies or Google professional associations or community groups that would be attractive or advantageous to your target users.