With FireChat, you’ll be able to chat with anyone close to you location-wise, even when there’s no WiFi or when you’re outside the coverage area of your mobile network. It works by making use of the Multipeer Connectivity Framework built into Apple’s iOS 7. Think of it as being a peer-to-peer WiFi-Bluetooth connection of sorts where you’ll be able to send text messages and even images without the usual service or connectivity requirements.
FireChat works best in “Nearby Chat” mode where you have to be within 30 feet of the person you’re chatting with. The app is available for free on iTunes.