1. You don't need to have a good reason to text someone
2. You can contact someone without having a long conversation
3. They're portable (provided you remember to charge your battery!)
4. You can stay in touch with people who don't feel like having phone coversations (eg overdue pregnant friends.... I know I didn't answer the phone for days at a time when I was overdue!)
5. You can get away with terrible spelling
Want to add anything?