How to send regular Hangouts message instead of SMS? By default Hangout send messages via my carrier as SMS. It's OK for me in most cases, but sometimes I want to send message (with photos, for example) to a another Hangouts user and not want to paid for this. How to send regular Hangouts message instead of SMS?
If your recipient is also a Hangouts user, you can switch between SMS or Hangouts message before sending the message.

From Google Hangouts support: 


  Switch between Hangouts messages and text messages
  
  When you're sending a message in a merged conversation, you can switch between sending a text message to a person or sending a Hangouts message.
  
  
  Open the Hangouts app on your Android phone.
  Open a new Hangout or text conversation, or an existing one.
  Touch the Hangouts or text message icon at the bottom of the screen. When you view the Hangouts icon, you can also see whether the person is available. The green icon means that the person is available on the Hangouts app on a computer or mobile device.
  
  
  To send a text message: Touch the SMS icon .
  To send a Hangouts message: Touch the Hangouts icon  .
  
  Type your message in the empty box of the conversation screen.
  Touch the send icon  .