I can see the value of Information Sharing Agreements for a plan with more than one participant, but I'm restating a plan for a one-man not-for-profit. Does he need to get one of these signed for each vendor he uses for his plan assets? He doesn't have a loan or hardship provision in his plan.

By the way -- since our firm is restating his plan, do we need to have an Information Sharing Agreement with him, too?

An info sharing agreement per se is only needed with those 403b vendors to which an 'exchange' inside the 403b plan is made after 7/24/2007. Treas Reg § 1.403(b)-10(b)(2)(i)(C)

As for 403b vendors that will be receiving new contributions after 2008, a prudent employer will have an agreement that specifies that the 403b contract is maintained pursuant to the employer's 403b plan (and subject to the plan's terms and the employer's amendments to the plan), and which defines what the 403b vendor will be doing, part and parcel to a delegation of compliance duties per Treas Reg § 1.403(b)-3(b)(3)(ii).

He is not the non-profit.
He is not the employer.
He is not the plan sponsor.
He is not the plan.

He, the individual has nothing to do, per se, with what might be required of the plan, the employer, the plan sponsor or any service provider.

I doubt that it matters for most things whether it is for one man or ten.