IMHO this is probably the first! thing you should do. To my own surprise people will give you money for your service even if you don't have a websites (and name, logo, slogan or anything else), and you send your 'product' via email.
And 3 out of 4 ideas don't survive these 20 calls - so you'll save a lot of time if you sell first and build later.
Emotionally that's not easy - of course - but it's what you will be doing all day anyway if it goes well, so why not start early?