[dfox]

Compression is inherent feture of WAP and some WAP browsers could use the WAP infrastructure to transfer not only WML, but also well-formed XHTML.

[lxgr]

Opera Mini went way beyond just compression. It effectively rendered the website server-side and then sent optimized markup to the client (so it's much closer to "print site to SVG" on the server than "Content-encoding: gzip").