Before I get into what works and doesn’t for SMS messaging, I wanted to first note the difference between emoticons and emoji.
Emoticons are faces created mostly from standard keyboard characters – GSM characters. Examples are 😉 🙂 😀 . You’ll recognise them for sure. They were created about 34 years ago by an engineer who felt there needed to be a way to let people know you’re being funny or joking in an email message. Since then they’ve grown to be near-universal symbols of many happy or sad emotions and are often replaced by picture versions – depending on the program being used to view them.
Emoji on the other hand are a standard set of characters used to depict all sorts of images from country flags to flying ducks. They are based on the Unicode character set. How each emoji appears depends on the platform and the fonts installed, though what each one means (the name usually) remains the same. The emojipedia.org website says there are 845 emoji characters that are commonly supported across messaging programs, but that iOS 9.1 supports 1,620. That’s nearly double the common set, which makes the issue of compatibility clear.
Getting back to SMS messaging, emoticons are generally supported across most networks and phones using the GSM standard. But there are some characters that take up extra space.
The extended characters require two character slots rather than one. A normal GSM SMS message can have 160 characters. If you type the following a smiley emoticon, :), you’ll have used two characters so you have 158 more. But if you want to use a big mouth happy face like this :] or :} it will count as three characters and you have only 157 more. Both the ] and } are part of the extended set.
If you decide to use the extended character set (whether in emoticons or not), you’ll have fewer characters left for the rest of your message. But that could be well worth it to send the perfect emoticon.
To see what characters are in the basic set and which are extended, you can view this page that includes a table of all the characters.
But what this also means is that you can likely send emoticons safely over SMS to most networks and phones. How they appear will depend on how the handset decodes the emoticons. It may change the basic smiley to a yellow smiling happy face. Or it may appear just as the characters. But in both cases the reader will know what you mean.