Mig33 is an exciting new company that's bringing social networking to mobile phones.  They have a combination of fun technologies that enable mobile communities to keep in touch with friends, family etc. They offer  a combination of VOIP calls, text messaging, IM, chat rooms, email and social networking .  Using their system, users can create profiles, share photos and do a lot of the fun things that most people are currently doing on traditional social networking sites like Myspace and Facebook. I recently met them at the DemoFall 07 Conference where they were one of the Demo God Award winners.
Their service is now in beta in over 200 countries and in a short period of time have got more than 6 million users sharing photos, exchanging messages and networking with each other.  With the current popularity of social networking sites especially among teenagers and with more than 2 billion mobile users worldwide, the market opportunity is huge. They are currently funded by Accel Partners, Redpoint Ventures and Technology Venture Partners.  I believe they are disruptive as they can deliver their services directly to mobile phone consumers without needing the carriers.  We have all been waiting for the next  killer mobile app that consumers will gravitate towards and mig33 may have built just that.   Their product is currently built on the J2EE stack.  You can find out more information about this company at http://www.mig33.com.