If an individual to whom subsection (a) or (b) applies estimates that the amount which will be available for deduction under such subsection for any premium payment period will be less than the amount of the monthly premiums for such period, he may (under regulations) pay to the Secretary such portion of the monthly premiums for such period as he desires.
In the case of an individual who participates in the insurance program established by this part but with respect to whom none of the preceding provisions of this section applies, or with respect to whom subsection (c) applies, the premiums shall be paid to the Secretary at such times, and in such manner, as the Secretary shall by regulations prescribe.
Amounts paid to the Secretary under subsection (c) or (e) shall be deposited in the Treasury to the credit of the Federal Supplementary Medical Insurance Trust Fund.
In the case of an individual who participates in the insurance program established by this part, premiums shall be payable for the period commencing with the first month of his coverage period and ending with the month in which he dies or, if earlier, in which his coverage under such program terminates.
In the case of an individual who is enrolled under the program established by this part as a member of a coverage group to which an agreement with a State entered into pursuant to section 1395v of this title is applicable, subsections (a), (b), (c), and (d) of this section shall not apply to his monthly premium for any month in his coverage period which is determined under section 1395v(d) of this title.
In the case of an individual enrolled in a Medicare+Choice plan, the Secretary shall provide for necessary adjustments of the monthly beneficiary premium to reflect 80 percent of any reduction elected under section 1395w–24(f)(1)(E) of this title and to reflect any credit provided under section 1395w–24(b)(1)(C)(iv)  of this title. To the extent to which the Secretary determines that such an adjustment is appropriate, with the concurrence of any agency responsible for the administration of such benefits, such premium adjustment may be provided directly, as an adjustment to any social security, railroad retirement, or civil service retirement benefits, or, in the case of an individual who receives medical assistance under subchapter XIX for medicare costs described in section 1396d(p)(3)(A)(ii) of this title, as an adjustment to the amount otherwise owed by the State for such medical assistance.