I read this article from T-Mobile UK about a shift of mobile broadband from contract to prepaid offerings. Strange it's taken them this long to realise....
... and what is also interesting is what this means for the 3G-enabled notebook market. With prepaid options, it is incumbent on the end user and PC vendor deciding to spec their notebooks with an HSPA card at the time of purchase. Otherwise they'll just use a dongle instead.
To be honest, I'm actually expecting even "plain vanilla" prepay to shift towards other options like 3rd-party paid services, or "free" (ie sponsored) models similar to some WiFi hotspots. If we can somehow get rid of the need for a physical SIM, we could also move to ad-hoc models much more easily too.
All this is quantitatively analysed in a lot of depth in the recent Disruptive Analysis report on Mobile Broadband Computing. Please contact info AT disruptive-analysis DOT com for more details and pricing.