For quick communications, we have iMessage and a host of other messaging apps, each with varying degrees of security. Apple has claimed iMessage is extremely secure, but that claim has been questioned. Wickr says it can top them all with a free iOS app containing military-grade encryption (AES256, ECDH521, RSA4096 TLS). Even better, the Wickr servers do not have the keys to decrypt your messages.
You can also set expirations on messages so they'll disappear after a pre-determined amount of time. Just like iMessage and most other messaging apps, there is no charge for the Wickr service; the app is free, and messages are delivered over the internet at no cost. The app also allows you to attach videos or photos from your camera roll, or images that are taken directly using the app camera controls.
Metadata is not shared so time, location and any identifying tags are deleted. Wickr claims the app is made with best-in-class security technology, so no two users will ever have the same encryption key and the key is destroyed upon use by the sender's phone.
I tried the app and it worked well. Delivery was a bit slower than real time or using iMessage, but it was still prompt. The picture send function worked fine. I can't really test the security of the app, but the people involved with the creation of the app and the names on Wickr's advisory board are impressive. You can get more information and an extensive FAQ on the Wickr webpage.
About the only potential issue with the app is that before your message expires, the receiver can grab a quick screenshot. However, the Wickr FAQ states that: "To make it harder for people from taking screenshots of photos and videos, we have programmed the app to stop showing a photo or video when the device is moved by a certain amount. To view the media, use a steady hand."
Wickr is easy to set up and use. Of course, both sides of the messaging transaction need to run the Wickr app.
One of the nice things about iMessage is that I can use it from my Macs at home or on the road. There is no Mac client for Wickr, but I would love to see one.
Wickr is not a universal app, but will run on an iPad (not at full-screen unless you are in 2X mode). Wickr requires iOS 5.1 or greater and is optimized for the iPhone 5 series.