(a) A request for enrollment is required of an individual who meets the eligibility requirements of § 407.10 and desires SMI, if the individual—

(1) Is not entitled to hospital insurance;

(2) Has previously declined enrollment in SMI;

(3) Has had a previous period of SMI entitlement which terminated;

(4) Resides in Puerto Rico or outside the United States; or

(5) Is enrolling or reenrolling during a special enrollment period under § 407.20.

(b) A request for enrollment under paragraph (a) of this section must:

(1) Be signed by the individual or someone acting in his or her behalf; and

(2) Be filed with SSA or CMS during the initial enrollment period, a general enrollment period, or a special enrollment period as provided in § 407.20.