Become familiar with SMS language first. To send a romantic SMS, you must first know what it is you're sending. Know, for example, that “gr8” means “great” and “luv” means “love.” You must first know the language before you can send any SMS message.
Think about what you want to say before you attempt to send a message. Remember that all you're really doing is converting one language to another (even though both are technically English). Imagine that you're sending a regular message to your significant other and creating a romantic SMS should be a breeze.
Keep the actual message short. The “short” in SMS may refer to the shortening of words, but you should keep the message brief. A sentence in SMS language can be cute, but an entire paragraph full of “2mro,” “u” and “thx” can get very obnoxious in a hurry.
Use symbols to make the romantic SMS cute. You want the person on the receiving end of the message to chuckle and at the same time know what you're trying to say. Use “:)” to let the person know that she makes you smile. End the message with a “<3” to emphasize that you love her.