Use Messages to send text and picture messages to your friends, family, or other contacts. When you use Messages, your texts and pictures are sent two different ways and if you use Straight Talk or Net10 Wireless you should understand the difference.
Like any other smartphone, Messages send standard SMS(text messages) and MMS (picture messages) to any other cell phone user. If you use the Apple iPhone and your buddy or sweetheart uses a Samsung Galaxy S III, your texts and pics are sent and received using SMS and MMS. If you may remember fondly how AT&T, T-Mobile, or Verizon and the rest charged you a little fee per message or flat fee per month for unlimited messages.
Messages can also deliver your Messages using iMessage. iMessage is an Apple service that lets you send texts and pictures to other iPhone, iPad, iPod Touch, and Macintosh users. The service is unlimited and free if you are using your iOS device on a Wi-Fi connection. It will also use your cellular data connection to deliver messages and the cost for that depends on your data plan.
To use iMessage you need to turn in on in the Messages settings. It uses your Apple ID, email, and cell number to connect you to other users using iMessage.
If you look carefully in Messages, you can see if your text or picture messages was delivered using SMS/MMS or iMessage. Messages sent using SMS & MMS appear in green. Also notice that Messages shows the the message is a text messages (SMS) in the second screen.
Messages sent using iMessage appear in blue.
This is why if you are using Straight Talk or Net1o Wireless you often can send and receive text and picture messages with other iPhone users but not people using other iPhones.