Phone company records are difficult to obtain. I say difficult, not impossible. Even with a validly issued civil subpoena, the phone company will not comply without a notarized written consent from the consumer who “owns” the phone number. You need a signed and notarized form such as this: Sprint Consent to Release Information
Pub. Util. Code, § 2891 provides:
(a) No telephone or telegraph corporation shall make available to any other person or corporation, without first obtaining the residential subscriber’s consent, in writing, any of the following information:
Code Civ. Proc., § 1985.3
(f) A subpoena duces tecum for personal records maintained by a telephone corporation which is a public utility, as defined in Section 216 of the Public Utilities Code, shall not be valid or effective unless it includes a consent to release, signed by the consumer whose records are requested, as required by Section 2891 of the Public Utilities Code.