As discussed at Flyertalk.com, Hilton is offering complimentary Gold status (details of Hilton status here). Just dial 1-800-HHONORS, ask for a customer service representative, and tell them you are calling about promotion code CTCH.
This seems to work for most folks, and provides or extends Gold status instantly.
The promotion is apparently with Citibank, with elite HHonors membership offered to Citibank members with special Chairmans status of some kind. However, the promotion code is currently mentioned in the main recording on the Hilton 800 number so it really isn’t a secret. This is likely just a mistake on Hilton’s part to publicize it this way.
Some folks report problems signing up for the promotion, with representatives saying you need a letter from Citibank or asking whether you have a Citibank credit card, so your mileage may vary on the offer. If asked how you heard about the promotion you can honestly say “from the recording when I just dialed your 800 number.”
Update: CTCH worked perfectly well for me, and for folks who’ve left comments. Some people report on the Flyertalk.com thread that CTCH is technically for new Hilton HHonors members, and that CTCG is for current members. So if CTCH gives you difficulty with your existing account, you can ask for CTCG instead. Or if all else fails, open a new account with CTCH and merge it with your existing one.