SMSTO: and why the format matters
There are two competing encodings. SMSTO:number:message comes from the same de facto family as the WiFi and MECARD formats and is understood by essentially every scanner. The RFC 5724 form, sms:number?body=text, is the standards-track version but has patchier handling of the body parameter across apps.
This generator emits SMSTO:, which is why a pre-filled keyword survives on the widest range of devices. If you have ever scanned a code that opened an empty message thread with the right number, you have met a scanner that recognised the number but discarded the body.
Write the number the way a stranger's phone needs it
Use full international format with the country code — +60 12 345 6789, not 012 345 6789. A national-format number works for a local handset and fails for a visitor whose phone assumes a different country, which is the exact audience a sign in a hotel lobby or airport is aimed at.
Spaces and dashes are cosmetic; the messaging app strips them. What matters is the leading plus sign and country code. Shortcodes are the exception — they are national by definition and cannot be dialled internationally, so a code built around one only works domestically.
Keywords, opt-in and the message you pre-fill
Keyword campaigns are the classic use: a single word like JOIN or QUOTE that your SMS platform routes on. Pre-filling it removes the two failure modes of printed campaigns — mistyped keywords and mistyped numbers — and costs nothing to produce.
Keep the pre-filled text to one short line. It is a starting point the person can edit, and a long pre-written paragraph reads as something to delete rather than send. Where consent matters, remember the tap-to-send step is what makes the opt-in the person's own action rather than yours.
SMS against the alternatives
Against a phone call code: messaging works when the recipient cannot take calls, leaves a written record on both sides, and is far less intimidating for a simple enquiry. Against an email code: SMS reaches a phone that has signal but no data, and gets read faster.
The costs are real though. Messages may carry a charge for the sender, particularly internationally, and there is no delivery guarantee. For anything with a long or detailed response, a link to a page will serve the reader better than a thread of texts.