In a patent app made public this month, RIM's lab geeks describe setting up a proxy server right on the phone that would intercept the browser's web requests and bundle, compress, and send them to a gateway on the other end (BIS, we presume) that would know how to deal with the packet.
Likewise, compressed data would be sent back to the proxy, which would expand and deliver standard HTTP to the browser, just as it would normally expect.