You can use your iPhone to send text messages. Text messaging, for those who haven't used it, is a good way to send a quick message when you don't have time for a phone call.
Tap the Text (SMS) icon on the Home screen to launch the Text application, and then tap the little pencil and paper icon in the top-right corner of the screen to start a new text message.
The To field becomes active and awaits your input. You could do three things at this point:
If the recipient isn’t in your Contacts list, type his or her cell phone number.
If the recipient is in your Contacts list, type the first few letters of their name. A list of matching contacts appears. Scroll through it if necessary and tap the name of the contact.
The more letters you type, the shorter the list becomes.
Tap the blue plus icon on the right side of the To field to select a name from your Contacts list.
There’s a fourth option if you want to compose the message first and address it later. Tap inside the text entry field (the oval-shaped area just above the keyboard and to the left of the Send button) to activate it, and then type your message. When you’ve finished typing, tap the To field and use one of the preceding techniques to address your message.
When you have finished addressing and composing, tap the Send button to send your message on its merry way.