What is an informal method of communication relevant to routine business?

A memorandum is a commonly used informal method of communication, especially in routine business settings. It often serves as an internal memo that can convey information quickly and efficiently to relevant parties within an organization. Memorandums typically discuss updates, directives, or informal communications that do not require the formality of a letter or a more structured format.

In contrast, the other options, while they are indeed communication methods, may not be regarded as informal. Email can be both formal and informal, depending on the context and tone. Telephone calls, while personal and immediate, can carry a more formal tone, especially in a business context. Face-to-face meetings often involve structured discussions and agendas, making them typically more formal than a memorandum. Therefore, a memorandum stands out as an accessible way to communicate routine business matters without the formalities required by other methods.