> The biggest fault (besides being proprietary) is that you must be online in order to use WTW.

That doesn't seem to be the case anymore.

It's still not a great system – many included words are ambiguous (e.g. English singular and plural forms are both possible, and an "s" is notoriously difficult to hear over a bad phone line), and it's proprietary, as you already mentioned.

It's definitely not the case, as the word list and algorithm are not secret (notwithstanding that they're proprietary) and have been re-implemented and ported into at least a couple of languages that allow for offline use. I have a Rust implementation that started life as a transliteration from Javascript. I wouldn't recommend using it, still -- I wrote it in the hope of finding more problems with collisions, not because I like it.