Interesting article here about the impact of email and other background applications on mobile networks, commenting that regular polling of servers generates an increase in signalling traffic, even if the actual data being transferred is in small chunks.
This fits in with a theme I've been hearing a lot about recently - it's not just about the GB of data, there are other "resources" that need to be managed. Various people have also talked to me about power-control messages, number of separate parallel TCP connections and so forth.
This is likely to cause some interesting headaches for policy management and future business models - it's one thing to say (perhaps) that someone should pay for 10GB of video traffic traversing a network with a high QoS. At least there's a fair chance that all involved understand what that means, even if they don't like it.
But trying to tell application developers or content providers to keep a lid on their apps' consequential signalling traffic is a bit of a tall order, especially as it will probably be highly dependent on both the type of phone, and the precise way a given network has been configured (timeouts, power setting etc).
Separately, I've commented before that always-on applications also have a tendency to kill handset batteries, as they keep the radio in a high-powered state.