Further to my earlier post, I know that one of the "major UK 737 operators" to which I referred does not have a squat switch inhibit for WAI on the ground, and I'm fairly certain that the other operator doesn't either. I find it hard to believe that this switch is a Boeing option, as usually Boeing are fairly dogmatic about how to operate their a/c, but it seems from other postings that it is indeed an optional extra. At the option of each airline, or each licensing authority? If the latter, what about JAA?
Boeing has no objection to use of WAI after anti-icing; the previously-thought idea that WAI bakes the fluid into a solid coating is not correct, apparently the fluid dries into a fine powder.