29 CFR § 2550.403b-1 - Exemptions from trust requirement.
(a) Statutory exemptions. The requirements of section 403(a) of the Act and section 403a-1 shall not apply -
(1) To any assets of a plan which consist of insurance contracts or policies issued by an insurance company qualified to do business in a State;
(2) To any assets of such an insurance company or any assets of a plan which are held by such an insurance company;
(3) To a plan -
(i) Some or all of the participants of which are employees described in section 401(c)(1) of the Internal Revenue Code of 1954; or
(ii) Which consists of one or more individual retirement accounts described in section 408 of the Internal Revenue Code of 1954. To the extent that such plan's assets are held in one or more custodial accounts which qualify under section 401(f) or 408(h) of such Code, whichever is applicable;
(4) To a contract established and maintained under section 403(b) of the Internal Revenue Code of 1954 to the extent that the assets of the contract are held in one or more custodial accounts pursuant to section 403(b)(7) of such Code.
(5) To any plan, fund or program under which an employer, all of whose stock is directly or indirectly owned by employees, former employees or their beneficiaries, proposes through an unfunded arrangement to compensate retired employees for benefits which were forfeited by such employees under a pension plan maintained by a former employer prior to the date such pension plan became subject to the Act.