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The 4 Parts of an SMS Message

The great thing about SMS messaging is how simple it is. You just type, click send, and the other person gets the message almost instantly. But there’s more going on in that simplicity than you might realise. Each message has different parts. Let’s look at them individually so you’ll understand everything that goes into your message when you hit “send”.

Text Label

The text label is also called the “From” field or sender ID. It lets the person receiving the message know who sent it. Normally on a mobile, that field is filled in automatically with your mobile number. If the recipient has you as a contact, their phone will translate the number to the name they have listed for your number.

However, when you use an SMS service like fastsms, you often have the choice of filling in the text label with anything you want. Well, within limits. The field only allows 11 alphanumeric characters. That’s letters and numbers, but not spaces or special characters (e.g. $,%,:). Another important aspect of using a text label is that you will not be able to receive replies. Because of this, text labels are best for one-way messaging that you do not want or expect people to send replies to. This includes opt-out options.

If you do use a text label, it’s best practice to make it clear who the sender is. Use your company or organisation’s name. If that won’t fit into 11 characters, use an abbreviation or well-known alternative. Don’t try to be funny or cryptic. Your messages may get caught in spam filters or receive spam complaints if it isn’t clear who the sender is or if it appears suspicious.

Alternatively, you can use your virtual mobile number (VMN) as your sender ID instead of a text label. When you do, you’ll be able to receive replies and be easily identified by a consistent mobile number.

Message body

You guessed it. The message body is where your actual message goes. While you could go on and on, the character limit is 160 for a single SMS message. Those are GSM characters which are defined for use with GSM based mobile phones. Most of the usual characters like letters and numbers, only count as one character because they are included in the GSM definition. But some characters not included with GSM will count as two characters. This is because of how those characters are translated into bits when encoded and transmitted over the network.

Whenever you’re composing a message with NetMessenger (the name for our online SMS service) you’ll see a character count that decreases as you type. If you’re concerned about going over the character limit, it’s best to watch that number. That way you don’t have to worry about specific characters and how much they count – we’ll do the counting for you.

If you’ve already signed up for your free account and tried sending a message, you may have noticed our character count actually goes to 456. We allow you to write up to that many characters in a single text window, but our system will break it out into three messages when we send it. When the recipient gets it, their phone will put it all back together into a single message. So when 160 characters just isn’t enough, you can send more. Just remember that each 160 characters counts as a messages sent, even if you only click send one time.

The process described above for longer messages is called “concatenation”, or sometimes “linked messages”.  Different networks have different rules about how many messages they will link together when they are sent. So you might send 456 characters in a “single” message from fastsms, but if the network your recipient is on doesn’t support it, they’ll get three separate messages.

User data header (UDH)

If you’re the type that likes maths, you may have noticed that 160 times 3 is 480. Not 456. This difference is because concatenated messages require additional data to be sent so the recipient can put them back together. This data is sent in the UDH. It includes information about the sender and also the message sequencing.

So if you send a full 456 characters, the first 160 characters, minus what’s needed for the UDH will be sent out. The UDH will say this is message number 1 of 3 from sender xyz. Well, it will say that in encrypted computer speak (bits). The next one will update the UDH to say number 2 of 3 and so on.

When the messages reach the other end, the mobile will read the headers and put the messages in order into one single message – unless they are a network that doesn’t support it. But most do these days so feel free to chat up to 456 characters. Just remember it counts as three messages sent in your account.


Choosing a recipient is something even more simple than choosing a text label or VMN right? Generally, yes. But you also have options. NetMessenger has five different ways to enter a recipient, or more than one recipient at a time.

  • Manually entering a number
  • Contact from the address book
  • Group of contacts from the address book
  • A list of numbers
  • Or a one-off list we call a Campaign

Who knew you could have so many choices? These options make sending SMS with NetMessenger kind of like email. You’re probably more familiar with creating groups and lists (especially if you’ve used Outlook).

For each recipient you’ll still need their mobile number in international format, but using the address book lets you enter it once and forget about it. You can look up the contact by name later when you want to send. Have a lot of contacts? No problem! Contacts and numbers can be uploaded in bulk using a CSV file.

Once you’ve chosen your recipients, the networks do their magic to make sure everyone gets the right messages. Of course it isn’t really magic, but a complicated set of protocols and filters that direct each message to the specific mobile number. I’m just thankful all we have to do is pick a name or number and the hard work is done by our software and the networks!

There you have the four key parts of an SMS message. You probably know more than you wanted to, or maybe it piqued your interest to learn more?

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