All about SMS – characters, segments, senders and delivery
Understand business SMS: GSM-7, Unicode, concatenated segments, sender types, links and delivery statuses.
SMS, Short Message Service, is a standardised way to send short text messages through mobile networks. Businesses use the channel for reminders, operational information, one-time codes, customer service and marketing.
The experience is simple for the recipient, but several technical details affect how a message is counted, displayed and tracked.
160 characters only applies to some messages
An SMS using the GSM-7 character set normally holds 160 characters. Common Latin letters and digits are included, although some characters use two positions.
If the text contains characters outside GSM-7, including many other writing systems or emoji, the message is normally encoded as Unicode. A single Unicode SMS then holds 70 characters.
Longer texts are split into segments and usually displayed as one joined message on the recipient’s phone:
- GSM-7: 160 characters in one SMS, then 153 characters per segment,
- Unicode: 70 characters in one SMS, then 67 characters per segment.
Each segment is routed and charged as an SMS. Use the character counter in the API playground or in the web service where you create the message.
The sender can be a name or number
A business message can use:
- an alphanumeric text sender,
- a standard or virtual mobile number,
- other sender types depending on the country and operator.
A text sender provides clear branding but normally cannot receive replies. Use a receiving number when recipients should be able to respond. Sender rules vary by country, and some markets require advance registration.
Read more about senders and settings.
Links extend the short message
SMS does not provide advanced layouts, but a link can lead to:
- a booking or confirmation,
- a mobile-friendly campaign page,
- a payment or order page,
- a survey,
- more detailed information.
The link should lead directly to the right destination, and the page should work well on mobile. For campaigns, trackable short links can shorten the message and provide click statistics.
Accepted does not mean delivered
When a service or API accepts an SMS, it means the message has been received for processing. It does not confirm that the phone received it.
A typical flow is:
- the sender submits the message to an SMS Gateway,
- the message is validated and routed to the mobile operator,
- the operator attempts delivery to the phone,
- a delivery report updates the status.
The phone may be switched off or outside coverage, delaying the final status. Incorrect numbers, disallowed senders and operator filtering can also stop delivery.
Use the complete status-code guide when troubleshooting a message.
Choose a service that matches the workflow
iP.1 provides several ways to use the same mobile channel:
- Web SMS for manual messages, contacts and conversations,
- One Channel for planned campaigns across channels,
- SMS API for event-driven messages from a system,
- Mail2SMS for SMS from an email workflow.
For a campaign, continue with SMS marketing in four steps. For automated messages, start with Get started with SMS API.