Some users have reported problems with sending text messages to their friends and family after the upgrade to iOS 7.
Typically, when iMessage is unavailable, your iPhone should send messages as SMS ones instead, denoted by the green chat bubble as opposed to the regular blue.
If, however, your iPhone won’t send texts automatically, here’s a possible fix.
Tap into the Settings app, and scroll down to tap on Messages. Once there, you’ll see a toggle switch for Send as SMS. Set this to ON with a quick tap and your iPhone will start sending messages as SMS ones without you needing to intervene.
Even with this toggled OFF, you can still send messages when they stall out with iMessage. Simply tap and hold on the message mid-send, and choose Send as Text Message from the popup menu that appears.
Now you can send iMessages to those with an iOS or Mac device, but still communicate with anyone using an Android or feature phone (ugh).
Via: Digital Trends