An SMS short code is a five- or six-digit number that sends and receives text messages for an organization instead of a person. Delivery notices, bank alerts, sign-in codes and text-to-donate campaigns in the United States usually come from short codes. The codes are called common short codes because a single code works on all the participating carriers, so a customer on any major network can text the same number.
Five digits or six
Five-digit codes run from 20000 to 99999 and six-digit codes from 200000 to 999999, according to the Short Code Registry’s FAQ. Neither length is technically better. Five digits are easier to remember, which suits a code printed on a poster or a receipt. Six-digit codes turn up often on programs that only send, such as fraud alerts, where nobody needs to remember the number.
Who hands them out
The codes are leased, never sold, through the Short Code Registry, which the Common Short Code Administration runs under CTIA, the wireless industry association, for the U.S. carriers. A lessee picks a specific number, called a select or vanity code, or takes one the registry assigns at random. In 2016 the registry’s rates were $1,000 a month for a select code and $500 a month for a random one, on terms of three, six or twelve months.
The lease alone does not switch anything on. Each carrier has to approve the program that will run on the code before messages flow on its network, and the approved program then has to keep to the rules in CTIA’s Short Code Monitoring Handbook, which the industry audits against. Clear opt-in and working HELP and STOP replies are the core of it.
Dedicated and shared codes
A dedicated code serves one brand or organization. A shared code is leased by a messaging provider and used by many of its clients at once, with each client’s program kept apart by keywords. A dentist’s reminder service and a gym’s class alerts could sit on the same shared code, one answering to the keyword SMILE and the other to LIFT. Shared codes cost each client far less, and the tradeoff is that one misbehaving client can bring carrier scrutiny down on everyone else using the number.
How a short code differs from a phone number
Ordinary 10-digit numbers, called long codes in the trade, were designed for conversations between people. Carriers can filter or slow a business that pushes large volumes of automated traffic through them. A short code is built for that traffic: it is vetted in advance and can deliver high volumes quickly. It is also national. A U.S. short code works only on U.S. carrier networks, and a phone on a foreign SIM card generally cannot reach it.
Most short codes bill at the subscriber’s normal messaging rate. Premium codes, which once added charges to the phone bill, were cut back sharply after the major carriers stopped billing most premium texts in late 2013; charitable and political donations were the main exceptions left. A few programs go the other way and are free to the user on the major carriers, which is how Crisis Text Line’s 741741 works.
The uses cover one-time sign-in codes, account and shipping alerts, appointment reminders, marketing clubs, polls and donations, and many programs send picture messages as well as plain text.