Introduction to SMS

  • Updated

With SMS, you can use mobile marketing, for example to reach new target groups or to reach your customers prominently on mobile devices. For interactive direct communication with customers, use it to receive incoming SMS. Optimizely's portfolio includes generation of short codes and standard numbers for two-way, mobile customer communication.

In most countries where this is possible, Optimizely SMS uses direct routes to network operators and offers exceptional quality, speed, and availability. Thus, Optimizely SMS is suited to the delivery of transactional and commercial messages.

A personalized message is possible at all times. For effective international SMS communication, Optimizely supports relative character sets and data formats, which support country-specific characters.

For example, use SMS to send:

  • appointments
  • PINs
  • billing, delivery or order information
  • personal and customized special offers

The sending of SMS messages requires a special opt-in.

Text length and number of characters

SMS messages are pure text messages. The maximum number of characters per message depends on the coding and special characters. Modern mobile phones can receive SMS messages which are too long (concatenated SMS) with no problem, and display these as a single message.

GSM character set

The GSM 7-Bit default alphabet was developed for sending and receiving SMS via the cellular mobile network. This standard contains a simple character set for sending SMS messages of up to 160 characters. The following characters are available:

"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_¡£¤¥§¿ÄÅÆÇÉÑÖØÜßàäåæèéìñòöøùü the following non-visible characters:

  • space
  • new-line
  • carriage return

The GSM standard character set includes an extension. Each character in the extension requires two characters:


UCS2 character set

The sending of SMS via Optimizely Campaign also supports the UCS2 character set. This set covers most modern languages, as defined in International Standard ISO/IEC 10646. See Universal Coded Character Set.

When UCS2 is used, an SMS message cannot exceed 70 characters because each character requires 16-bits; more than double the storage required by a character in the GSM 7-bit default alphabet.

Determining which character set is used

The characters in an SMS message determine if it is GSM-coded (7-bit) or UCS-coded (16-bit). Each SMS can have only one encoding, which is performed automatically. If an SMS uses one 16-bit encoded character, the entire message is 16-bit encoded, even if other characters can be encoded using 7-bit.

Country-specific features

The sending of SMS, subject to country-specific regulations, primarily includes these functions:

  • Sender identifier
  • Sending length (multi-part) SMS
  • Supported character sets

Moreover, as the customer, you are likewise subject to restrictions which vary by country. For example, you must comply with country-specific regulations on consent to advertising, privacy and competition regulations.


  • Optimizely does not support the delivery of binary content, such as ringtones or images.
  • Optimizely does not support certain mechanisms in language tables for Portuguese, Turkish, Bengali and Hindi, the locking-shift or single-shift tables in GSM standard.
  • Not every character is available in every country.
  • In some countries, the characters used are restricted by law or network operators. Moreover, especially among discount telephone operators, the characters in an SMS may not be delivered correctly. This can lead to display errors.

Multipart SMS (concatenated SMS)

You can send a message with more than 160 or 70 characters (depending on character set), but the text is sent as multiple, individual SMS messages. Modern devices may display these SMS messages as a single SMS. The previous procedure corresponds to the GSM protocol Concatenated SMS. For longer texts, several individual SMS messages are used and counted for billing purposes.

The maximum number of characters per SMS is reduced for concatenated SMS messages. Thus, only 153 or 67 characters (respectively) per SMS are available. The maximum lengths appear in the following table:

SMS encoding max characters per 1 message max characters per 2 messages max characters per 3 messages max characters per 4 messages each additional
GSM 7-bit (default alphabet) 160 306 459 612 each plus 153 characters
UCS2 70 134 201 268 each plus 67 characters

Recommended maximum number of characters

Do not send more than 10 SMS messages 1,530 characters) for a Concatenated SMS. If you send more than 10 SMS, or 1,530 characters, a multiple part message may not be sent or received correctly.

Field functions and placeholders in SMS

If you use field functions and placeholders in an SMS message, the text length of the SMS sent cannot be calculated in advance. If placeholder text is replaced by personalized content (for example, the recipient name), SMS messages may become multi-part messages and incur higher costs. So, before sending, check how many characters are included in your datasets and how long an SMS can be. You can also read the example in the Personalizations section.

Checking costs

Billing is calculated per SMS sent. For example, for a two-part SMS mailing, two text messages (SMS) are billed per recipient.

For a cost overview, Optimizely Campaign lets you enter the number of SMS messages – and thus the maximum number of characters – you want to send. If the text is too long for the selected setting (for example, 160 characters (1 part)), an error message is displayed.

Sender identification

SMS is implemented based on phone provider. In addition to telephone numbers, you can use up to 11 alphanumeric character strings as sender identification. with Optimizely SMS, you can use the following sender identification formats:

  • Alphanumeric sender identification. String of letter and number characters. The sender identification must begin with a letter. Avoid the use of umlauts and special characters. Alphanumeric sender identifications can only be used to send (not receive) SMS.
  • Exclusive short codes. Short sequences of numbers, for example 23232, for direct two-way customer communication. See German Federal Telecommunication Network Agency (Bundesnetzagentur) for the short code format for Germany. You can use exclusive short codes only within the country where they were assigned. International routing is not possible.
  • Non-exclusive short code. A short code is simultaneously used by multiple service providers. You may provide keywords for response capability. You receive only forwarded messages that contain the keyword you provided.
  • Long code. A long code is a customary mobile number that you can route internationally. For example, +4915112345678. The advantages of a standard number are cost and international usability.

Personalizing messages

You can insert placeholders for recipient list fields (such as "Hello {first name}!") or field functions (for example, salutation logic) into SMS messages. Upon delivery, these are replaced by the corresponding name (such as Hello Andrea!) or salutation format (Dear Mr. Miller).

If you use placeholders or field functions, the display of used/remaining characters cannot provide precise results. This is because Optimizely Campaign can only determine message length after the placeholder or field function is replaced by the individual value, which occurs directly after sending. So, a message intended to be sent as a single SMS might be divided into two messages, which results in higher delivery charges.


The following message contains a placeholder for the recipient 's first name and has 163 characters:

Hello {firstname}! Have you checked out our current holiday dealsat yet? They are only available today (before midnight) in our web shop. Act fast!

When sending, the placeholder is replaced with the recipient’s name, and could look like this:

1) Hello Max! Take a look at our current holiday deals at!Only available today (before midnight) in our web shop. Act fast!

2)Hello Maximilian! Take a look at our current holiday deals at!Only available today (before midnight) in our web shop. Act fast!

In the first example, the sent message has 145 characters and is sent as a single SMS. In the second example, the message has 162 characters and is divided into two SMS messages, so two SMS messages are billed.

Analyzing bounces

You can analyze bounces from SMS recipients. A bounce is generated when:

  • the mobile phone is switched off or unreachable during dispatch
  • the mobile phone's inbox is full
  • the number is invalid or no longer in use

Blocking numbers with a blocklist

If you want to send SMS mailings via your client, the client's blocklist is adjusted accordingly. You can block complete numbers or specific parts of numbers (such as area codes). You should block satellite phone numbers, because the cost for such a message is substantially more expensive (more than 1 euro per SMS).

SMS processes

SMS processes enable your customers to request or stop a service by sending an SMS with a predefined keyword. For example, your customers can send an SMS with the keyword Help to request help or Stop to unsubscribe from promotional SMS. For more information, see SMS processes.