I just checked numberguru.com. I plugged this number in, and it said nothing about it being a number "not in existence". In any case, those are also phone apps, which is not the case for 800notes. If those apps have the features that you want, then use them.
Called and I amswered. They didn't say anything and hung up after 10 seconds.
Called back and it's a Google number. This means it was made from a computer or a phone thru the Google phone service. In other words anyone can use that survice to hide their identity and show this phone number instead. The number is to a computer located somewhere in LA.