Businesses commonly use SMS for brief communications that tend to fit into 160 characters (the standard limit for text messages), such as PIN code requests, appointment reminders, order confirmations or flash sales notifications.

The conciseness of text messages is part of what makes them so successful with recipients – the content can be easily digested within seconds, for instance. However, the character limit is sometimes seen as a downside of SMS by firms that need to transmit longer messages.

Fortunately, there's a way around character limit restrictions: concatenated SMS...

What is concatenated short message service (SMS)?

The word 'concatenated' simply means 'linked together'. A concatenated SMS message – also called PDU mode SMS – is where a traditional SMS has exceeded its maximum length, resulting in multiple messages that are seamlessly linked together. Hence, they appear as one long message.

How does concatenated SMS work?

When you send a text that exceeds the character limit from your personal phone, your mobile handset and your network provider carry out a process that divides your SMS into multiple messages and forwards them (individually) to the recipient's phone.

At the recipient's end, their phone will receive and reassemble those multiple messages so that they appear in the same order you sent them.

Usually, neither you nor the recipient will notice anything out of the ordinary has happened. The process is handled by mobile phones and networks and is invisible to mobile users. But in reality, there's quite a bit of technical stuff happening behind the scenes.

An SMS consists of two components: a header and a payload. The header contains instructional data for the network (the sender and recipient's phone number and the message type). The payload includes the message content.

Also stored in the header is a User Data Header (UDH) flag – an indicator that tells both the sending and receiving device whether the text is a single message or part of a series. And in the case of multiple messages, the UDH flag details the message order, so the handsets stitch the entire message back together in the correct way.

Sending concatenated SMS for business purposes

Businesses using text messages normally rely on an SMS messaging platform/provider that can handle bulk messaging and integrate with CRM systems. The SMS provider acts as an intermediary between a business and mobile network providers, providing the fastest and most cost-effective route to reach SMS subscribers.

If you're planning on using an SMS provider for business texting, it's essential to check whether they support concatenated messages, as there may be times when you need to send longer texts to customers than what the standard SMS character limit allows for.

For the record, Latin-based languages have a limit of 160 characters and use GSM encoding. Whereas non-Latin languages, such as Arabic or Mandarin, use Unicode characters, reducing the limit for SMS messages to just 70 characters. Therefore, if your business uses non-Latin languages, having the option for concatenated SMS is particularly crucial.

What does a concatenated SMS message look like?

This graphic below shows how a concatenated SMS looks compared to a text sent in separate parts. The one on the right is much easier to read, right?

Graphical respresentation of a traditional SMS and concatenated SMS

When should you use concatenated SMS?

Concatenated SMS is best used for important or urgent messages, where the information you need to transmit is essential for conducting business.

One example is customer service texts, where an agent has a two-way conversation with a customer to resolve a problem. In this case, the customer likely would appreciate having detailed information (more than you convey in 70 to 160 characters) in one complete message rather than reading the content in chunks.

Another example is emergency alerts. Suppose you need to tell a lorry driver about an unforeseen road closure that will impact the time it takes them to get to their destination? It wouldn't make sense to have this information transmitted in bits and pieces (and risk the message order getting mixed up) because the driver would need to react quickly and make changes to their planned route.

Concatenated SMS isn't recommended for marketing messages purely because it's not cost-effective. This is because each part of your message will be charged at the rate of a single SMS.

While your target audience will receive one lengthy message, your business will have to pay for two or three texts per subscriber you're sending to. You'd effectively be doubling or even tripling the cost of an SMS marketing campaign, and that makes getting a good ROI difficult.

Concatenated SMS messages with Messente

Here at Messente, we support concatenated SMS (both outbound and inbound messages). There's no limit on the number of message parts you can send, so you can rest assured that no matter your message length, it will appear to your customers or clients as one complete message, sent in the original, logical order you intended.

Discover Messente's easy-to-use messaging API today – get started for free.