Principles of SMS Design
Designing for SMS is an exercise in constraint.
This sparse, bare-bones medium offers a spartan challenge for designers and product managers to hone their skills and return to design fundamentals. SMS design makes explicit the wicked trade-offs between minimalism and establishing context, between clarity and natural language, between usefulness and brand development.
Two primary experiences designing for the medium of SMS have sharpened my design practice in other media. The first was a series of payments and commerce proofs-of-concept that combined SMS and voice for bottom-of-the-pyramid customers in Africa and Latin America. The second was the design of a system used at the outbreak of Covid to monitor out-patients at St. James' Hospital in Dublin.
SMS is linear, asynchronous, slow.
Design constraints mean that interactions must be well-thought-out and clear. As a medium, SMS offers two broad design families with which to create the user experience: conversation design or menu design. The use-case and user expectations should point to which of these families of design best fits the problem.
Conversation design mirrors human to human interaction with SMS. This more natural approach, when done correctly, makes the interaction and brand association more human, more personable. It can be seamlessly integrated with chatbots when users have internet access. These benefits come at the cost of complexity. Human conversations can and do wander. As chatbot designers know, humans say the most unexpected things. In an online setting, there is scope to clarify users’ texts - it is faster, and cheaper than SMS. In SMS, the guard-rails for conversation must be tighter.
Menu design is perhaps the ultimate limitation of these guardrails. It is a premeditated calcification of where these text interactions can lead. As such, it lacks the flexibility of dealing with edge-cases. It forces the user quite explicitly into using our mental model of navigating the service. These limitations are strict. The menu should be limited to a very few options; ideally 2-5, up to 9 at a stretch. And of course, menus are anything but human. They are faceless, artificial, bureaucratic tedious things. No brand has ever been improved by an SMS list of menu-options.
Some principles then:
Less is way more. Only the most essential product features should be included. Each additional menu item beyond 5, often has negative marginal utility. It degrades the user experience.
Spell it out. Unlike most mediums of communication, SMS offers few signifiers of what's possible. Potential actions need to be specified explicitly from one text to the next. Expecting users to remember common commands is unreasonable.
Expect spelling mstakes. Responses are prone to error and abbreviations. Numbering entries reduces the chances of error. However, long lists introduce their own possibility of error.
Expect delays. SMSs do not always appear when they should, or indeed in the order specified. Roaming in particular messes this up. Design for this frustration.
Say it again. SMS must allow for the fact that coverage issues may mean that texts do not get delivered. A resend option should be included.
Where do the edge-cases go? There's no cheap hyperlink to sweep all the details under the carpet. Or is there. User journeys that demand a switch in medium should be considered non-essential.
Cost and trust. Either you shoulder the cost of the SMS within your business model or assume that users will quickly learn to curb their use. Users are generally mistrustful of corporate texts and worry that they are being scammed. Even reasonable clarification texts become a major frustration.