Since modern technology plays an important role in our lives, you should include the topic in some of your lessons. There are 276 free, printable modern technology worksheets to choose from that focus on technology and you can even narrow your search as there are several subsections. This is a nice worksheet designed to introduce some SMS abbreviations to your students. It would be an especially good exercise to do with intermediate level high school students because they will be able to relate to the content of the worksheet the best. By asking your students for their opinions, you can engage them in the material more than if you only ask them to answer multiple choice and true or false questions. If this is not a good fit for your ESL class, consider using one of the other available worksheets.
The extent to which you cover this topic in your course will depend a lot on your students. If you are teaching at a school with limited resources where none of your students have cell phones or personal computers, some basic vocabulary will probably be sufficient while if these things play a pivotal role in the lives of your students, they will be of more importance. You can talk about the amount of time students spend using different pieces of technology with any level learner and should consider asking advanced students to explain both the advantages and disadvantages of technological advances.