Transients and individuals waiting to get PO Boxes can request what free service?

The correct answer is General delivery, which is a service designed to assist those who do not have a permanent address to receive mail. This service is particularly helpful for transients or individuals who are temporarily in an area and need a secure way to collect their mail. General delivery allows customers to have their mail sent to a post office, where it can be held for a designated period until they can pick it up.

Other services mentioned do not provide the same type of support. Caller service, for instance, is typically used by those who want to have their mail held for pickup without needing a PO Box, while local delivery pertains to the distribution of mail within a specified local area. Firm holdout is a term related to the warehousing of mail for businesses or organizations that do not want to receive mail at a designated address but does not apply to individuals needing temporary mail services.