Your network operator might charge for MMS messages (where you insert a picture, video clip, etc.), but they shouldn't charge you for SMS messages that use Unicode characters (and EE don't), which can include the emotji from the built in keyboard (via the 😊 icon on the keyboard).
Be careful to watch the character count, as this will force Unicode mode, ...
Is your phone supplied by Ultra-mobile? Either way, you may need to tweak your APN settings. In settings > access point
I found some settings for Ultra-mobile on this site, I have no idea if they work:
Here's the settings:
Android settings for Ultra Mobile. These should also ...
Go to Settings->Networks & Settings->Mobile&SIM
Select SIM1/SIM2 Settings.
You should see MMS APN at the bottom of the screen.
Verify your MMS settings so that the following properties are as follows:
MMSC as http://mmsc.mobile.att.net
MMS as proxy proxy.mobile.att.net
MMS as port 80
MCC as 310
If no MMS APN is present then add a new one.