According to the Architects Practice Act, Section 5536.22 Written Contract, it says a contract isn't required when professional services are rendered when the client will not pay compensation.
Beyond doing pro-bono work for a non-profit, or for the good of the community, when would you do work for free? And, if doing pro bono work, wouldn't you use a AIA B106 (Standard Form of Agreement Between Owner and Architect for Pro Bono...)? Otherwise, who would you be doing free work for? I've always been under the impression that it was unethical for architects to offer to do work for no compensation. Isn't it unprofessional?