How do I send a message / text to an iPhone contact group?
Contact groups can help organize related contacts on the iPhone, but in iOS 7 these contact groups must be created using iCloud. Even when groups are synced to the iPhone, these default contact groups cannot be used to send a group text message.
iOS 7 does not have this feature built-in. Instead, there are several third-party apps that make it possible to send text messages out to contact groups. Here are some examples:
Connect - Contact Manager for iPhone (Free)
Group SMS ($0.99)
Text 2 Group - Quickly send messages for SMS & iMessage (Free, Pro $0.99)