I use WhatsApp, although I've found that I can't record HD video because them I'm limited to about 6 seconds (WA has a 12MB limit, and HD video records at approximately 2MB/sec.) Of course, the other person also has to have WhatsApp for this to work. Not a problem, because most people I know use WhatsApp, which is a fantastic alternative to SMS/MMS. It's like BBM or iMessage, but it's cross-platform.