I just stumbled across this interesting application for Windows Mobile. DeSofto Traffic Compressor for Windows Mobile is service that works via both a proxy server and an application that will install itself on your Windows Mobile as a network driver, and from there will compress both your incoming and outgoing traffic, unlike proxy servers which only deals with incoming traffic, and can deal with virtually all kinds of traffic, including mail and ftp.The compression ration can reach from 50-70% and even up to 90%, depending on the web-site and traffic type. It also acts as an anonymizing service for your smartphone.
While an app like this is much less necessary in this day and age of unlimited data plans, such plans are of course not universal, and sometimes come with ridiculously small caps (Orange, I am looking at you)
The application is sold on a subscription basis, with $7.95 buying you 8 GB/ year.
Read more about the app in our store here.