via e-mail or USPS (letter)
<Subscriber Name>,
Personal data on your <provider name> account was recently modified. If this change was made without your knowledge, please contact our customer support department at <customer support number> to confirm your PIN. This process helps us to protect your personal information. We sincerely appreciate your assistance.
Regards,
<Provider Name> Customer Support
via SMS (wireless only)
Information related to your <provider name> account has changed. If this change was made without your knowledge, contact customer support at <support phone number>.