Background info:
SBC's official statement - http://www.dslreports.com/shownews/72937

The guide:
1. The first thing you'll want to do is figure out the IP address of the site you're not able to get to. You can do this using the Windows command prompt (Start -> Run -> cmd):



The number listed next to the "Address" field is what you will be looking up.

2. After that, you'll need to know who owns the IP block of the site you're trying to reach. You can do this by checking ARIN, the corporation in charge of managing IP addresses in North America. Once you reach ARIN, paste the IP address in the "WHOIS" box near the top of the page. You'll see something like this: 
OrgName:    Net Access Corporation
OrgID:      NAC
Address:    1719 STE RT 10E
Address:    Suite 111
City:       Parsippany
StateProv:  NJ
PostalCode: 07054
Country:    US

ReferralServer: rwhois://rwhois.nac.net:43

NetRange:   209.123.0.0 - 209.123.255.255
CIDR:       209.123.0.0/16
NetName:    NAC-NETBLK02
NetHandle:  NET-209-123-0-0-1
Parent:     NET-209-0-0-0-0
NetType:    Direct Allocation
NameServer: NS1.NAC.NET
NameServer: NS2.NAC.NET
NameServer: NS5.NAC.NET
Comment:    ADDRESSES WITHIN THIS BLOCK ARE NON-PORTABLE
Comment:
Comment:    * Reassignment information for this network is available
Comment:    * available at whois.nac.net 43
RegDate:    1997-08-06
Updated:    2001-08-22

TechHandle: ZN77-ARIN
TechName:   Net Access Corporation
TechPhone:  +1-800-638-6336
TechEmail:  legal@nac.net

OrgAbuseHandle: ABUSE156-ARIN
OrgAbuseName:   Abuse Department
OrgAbusePhone:  +1-800-638-6336
OrgAbuseEmail:  abuse@nac.net

OrgNOCHandle: NOC270-ARIN
OrgNOCName:   Network Operations Center
OrgNOCPhone:  +1-973-590-5050
OrgNOCEmail:  network@nac.net

OrgTechHandle: AR97-ARIN
OrgTechName:   Rubenstein, Alex
OrgTechPhone:  +1-973-590-5101
OrgTechEmail:  alex@nac.net

OrgTechHandle: ZN77-ARIN
OrgTechName:   Net Access Corporation
OrgTechPhone:  +1-800-638-6336
OrgTechEmail:  legal@nac.net
3. To make the admin's job easier you'll probably want to include a traceroute. If you already know how to do one, skip this part and go on to step 4. If not, read on:
From the Windows command prompt (Start -> Run -> cmd), type tracert www.site.tld (where www.site.tld is a website, like www.dslreports.com. Below is a screenshot of a traceroute to www.dslreports.com.



4. Once you've gotten the correct WHOIS information for the IP address of the site you're having problems with, you'll have to contact its owner and let them know that there is a problem. The email address you need to contact is the one listed as OrgNOCEmail. Here is a 'sample' message you can modify for the site you're having problems with:

Hello,
My ISP, SBC/AT&T Communications, has recently acquired a new IP block from ARIN. Since this is a relatively new block, some providers have yet to allow users of this block on their network. I believe that this is why I cannot reach sitename.tld. My current IP is yourIP and below is a traceroute from me to the server I'm not able to reach:

traceroute

You can read more about it on SBC's official help site on DSLReports.com -- http://www.dslreports.com/shownews/72937

Thanks!
yourname
Note: If you don't know what your IP is, you can get it at http://www.dslreports.com/whois.
 If you have any trouble or have a suggestion you'd like to share, contact me via email at removed@dslr.net