Yes, I know it sounds like something from Dr Seuss, but the OED doesn’t actually begin with the first letter of the alphabet. There are 17 entries that precede it, all of which are numbers or incorporate numbers. The very first entry is in fact this one:
0800 number, n.
[O n.2 + EIGHT a. + HUNDRED n. + NUMBER n. Written with numerical symbol for the first element.]
A U.K. telephone number with the prefix 0800 which allows customers to call a business or information service without charge to themselves (cf. 800 NUMBER n.).
The earliest usage given is from 1988, which seems awfully recent to me. On the other hand, it does refer to the UK, so what do I know? The full list of numerical entries is:
0800 number, n.
0898 number, n.
800 number, n.
900 number, n.
Most of these were terms which I had encountered before, though some were new to me and others weren’t immediately apparent. “0898 number” is a rough equivalent to the “900 number” of the US, “101” refers to the common appending of that number to another word to indicate elementary knowledge (e.g., Economics 101), “1471” is a UK telephone feature that allows one to check on the last incoming call, “1984” refers societies of the type described in George Orwell’s novel of that name, “1992” was the year scheduled for the Single European Market and became shorthand for same, and “999” is the UK version of “911” in the US.
The surprises of this list are two-fold. First, and less surprising, is the inclusion of “4-H” and “4-H’er“, though that may well be the bias of my never having much to do with that organization. The other, much larger, surprise is that this list of numbers is so short. Having included these, I would have expected there to be other “words” that start with numbers. I can’t think off-hand of what these might be (indicating that they seem to have done a good job), but I expected more for some reason.