A dating site, for example... At what point is it considered "up and running" and how does that happen? Or a service referral site like task rabbit?
Totally agree with Jeff as well. I have been scaling software as a service product for the past 10 years and most experts will agree with me when I say that you need to get to 100 paying clients before you can really say you have a your MVP as Jeef explained (i.e. that has market value and fair potential).
Where do you start? By getting the first 10
Right now, as you are probably experiencing already, it is all about hustling, talking to ideal customers, showing your product, getting their feedback, implementing their ideas into your MVP, and doing this over and over until you get to 10 paying clients. Then you can start growth hacking and content marketing activities based on this early success.
Also, selling over the phone is great, but if you can meet these customers face to face, that's even better. You can't really build a relationship over the phone, at least not as good as in person. This step will help you build champions/ brand ambassadors, that will hopefully spread the word about your product, give you great testimonial, and agree to a case study (maybe a video one next time you meet them in person)
Nobody wants to be a guinea pig and most buyers will want to see demonstrated value before buying a newish product/service. Use these early customers as your social proof, and let their success stories do the selling for you.
Not sure about your price point, or even if you have a SaaS product. If you tell me more I can give you some quick metrics and pointers to help you along the way.
Best of luck!