As Slack/Skype and many others already exist you would need to find a compelling reason for businesses to adopt your offering instead and why it is worth the price. Then start by having a good website and use SEO so that the keywords of the problem you are solving mean people end up at your site. Give people a sign up form and then contact them to discuss what they are trying to do and how it might fit what you offer. Initial feedback should help you decide on your product viability and future changes.