A true picture of mobile messaging?

Yesterday Telecom NZ released some very interesting statistics showing which third-party instant messaging services are being used by their mobile subscribers.  For the month of May 2013...

• 150,000 used Apple's iMessage service
• 140,000 used Facebook messenger
• 78,000 used Viber
• 35,000 used Microsoft live messenger
• 32,000 used Skype
• 25,000 used Google Talk
• 23,000 used WhatsApp messenger

From the perspective of which services pose the biggest threat to carriers' SMS revenue streams, the numbers are quite surprising to me, particularly the dominance of iMessage & Facebook and the poor showing by WhatsApp (particularly given WhatsApp now has over 250m monthly users worldwide).  This got me thinking about why this might be, and I believe there are several contributing factors...  

1. App penetration will have a large influence on which services are used. iMessage is pre-installed on ALL Apple devices, while Facebook's ubiquity means users are likely to install FB Messenger even if they don't intend using it often.  
2. Telecom state that it is based on 'network data' from mobile subscribers.  From this, I am guessing they mean mobile data subscribers only, and exclude wifi data sent from mobile devices.  This would include however data-only plans for 3G-capable tablets and USB dongle-connected laptops.  You cannot run mobile-phone number dependent services (in this list Viber and WhatsApp) from these devices.
3. Apple iPads and Macbook Airs are likely to dominate the aforementioned 3G-capable tablet and dongle-connected laptop market, adding to the popularity of iMessage 
4. There are several services in the list that originated on the desktop - namely Facebook, MS Messenger, Skype, Google Talk.  I suggest that a decent proportion of mobile usage of these services is people just responding to messages sent by people from a desktop.
5. The majority of Telecom's smartphone users (which you must have to use the above services) are likely to be on post-paid plans.  Most of these plans include unlimited (or near enough to) SMS messages.  This means that texting is essentially free, making the use of WhatsApp and Viber redundant for in-country mobile to mobile messaging.

It would be interesting to know how many users are deliberately choosing to use these messaging services to contact other mobile users as a replacement for SMS.  The list might look quite different.  It is clear however that smartphone users are taking to a multitude of messaging services, and these are cutting into SMS's dominance of mobile messaging.  Who the ultimate winners will be is anybody's guess, but it is clear that the services that already have a large hooked-in audience and can translate across both mobile and desktop are in the front seat.