Excuse me, how can I send short messages to iPhone4s Unicom and iOS7. 1 system?

You can find the SMS icon in the iPhone4s phone, and then press Enter. After input, click the symbol in the upper right corner to create new information.

Then "Recipients" are displayed at the top of the new page. Enter the other party's mobile phone number in the "To" column, or click the "plus sign" at the back to look it up in your address book, click the other party's name after finding it, then enter the content to be sent, and click Send.