Wireless Intelligence, a UK mobile consultancy, has a very well written PDF file about Italian mobile operator TIM, that points out how SMS has slowed as the users are moving to Instant Messaging and Email driving more data plan sales for TIM.
This supports the kind of thing we're seeing with clients Palringo in the IM space and from Nokia with their new email client that went into public beta this past month.
Basically, if you give the public an easy to use, full-featured application for their mobile device that mimics the capabilities they are used to on the PC, you end up with better adoption.
As Wireless Intelligence writes, data plan adoption is increasing which means 3G is finally going to get its just due. Unfortunately, here in the USA 3G capacity is still going to be an issue until AT&T spends another chunk of change to increase capacity. All those new iPhones and new Nokia N and E series devices love to be on 3G networks, and the new applications that ride on them relish the added speed. With T-Mobile rolling out a new data network nationwide that delivers the same kind of speeds, but on different frequencies, the availability of 3G will only get better, and with that, a greater shift to these new applications.