Just received these tips in an email from AT&T:
If you believe you were the victim of identity theft, here are some steps you can consider for additional protection:
Close the accounts that you believe may have been tampered with or opened fraudulently. Use the Identity Theft Report, which can be found at www.identitytheft.gov
File a police report and get a copy to submit to your creditors and others who may require proof of the crime.
File your complaint with the FTC. The FTC maintains an identity theft database that law enforcement agencies use for investigations. Filing a complaint also helps the FTC better assist you, as the commission learns more about identity theft and the problems it creates.