The national "call before you dig" number that should be fully integrated by April.
The number was approved in March 2005 by the Federal Communications Commission, in an effort to eliminate confusion over which numbers to call to alert utilities of intent to dig. It is designed not as a replacement for the "one-call" centers already established, but as a hub to forward callers to the correct centers.
If your phone company has not yet changed its network so that an 811 call forwards you to the right place, you can always dial the one-call center directly. If you are unsure of that number, you can still call the existing "call before you dig" referral line at 888.258.0808.