Facebook allows you to instant message your contacts using a variety of devices including the iPhone, Android and Blackberry smartphones. You can also instant message your friends from the Facebook website. If your friend is logged into Facebook Messenger using their mobile device, you'll see a phone icon next to her name in your contact list.

Staying in Contact on the Go

If you want to send messages to your friends while away from your computer, download the Facebook Messenger app for your device. The app is available for the iPhone, iPod, Android, Blackberry, iPad and Android Tablets. Log in with the same username and password you use while logging in to the Facebook website. If you're not using a smartphone, you can still reply to messages sent to the mobile number you verified with Facebook just as you would with an ordinary text message. Facebook Messenger is available free of charge for all devices.

Checking the Status of a Friend

You can instantly see the status of your friends by looking at your contact list. Your contact list appears on the right side of the screen. Contacts who are online and available appear with a green circle to the right of their name. When you send a message to an online contact, it will show when the message has been delivered and read. Facebook Messenger will show when your friend is typing a message to respond to you. If your friend is using a mobile device, a small phone icon appears to the right of his name.

Sending Offline Messages

If you notice your friend is not logged in to Facebook or Facebook Messenger, you can still send her a message. Although the message won't be delivered instantly, it will be available for your contact to view once he has logged back in. Friends can be logged in to Facebook Messenger on a mobile device but become inactive if they're not using their device. A friend who is inactive will appear with a phone icon to the right of her name, with the amount of time she has been inactive displayed on the left. Inactive friends can still send and receive messages.

Considerations

Facebook Messenger sends data over the Internet. If you don't have an Internet connection, Facebook Messenger will not work. Data can be sent over Wi-Fi or cellular networks, and the phone icon displays next to contacts that are connected to the Internet and logged in on their mobile device. Some wireless companies may charge for the data usage associated with Facebook Messenger and may not count as text messages. You can send photos, audio messages and emoticons while using Facebook Messenger on a mobile device. Messages sync across the website and all devices you're logged in to.