http://www.e164.org is another root registry aimed at CC '1' while the ENUM LLC launches its 1.e164.arpa trials.
As for a list of companies that are participating in any registry, it's something I've yet to see anywhere.
i tried last week to call a u.s. 800 number using www.e164.org and freenum.org enum, which both point to tf.voipmich.com. in summary: it was impossible to get connected. looks like their gws are full or broken.
a service like that has to work reliably or it is good for nothing.
-- juha