Some care is warranted here:

Advice item #1 is plain wrong (when possible, serve the same content to all browsers). If you do this, the site will not work on the vast majority of the world's phones unless it is supremely lightweight.

There's a good reason why the best mobile sites out there use UA sniffing (Google, Facebook, Yahoo! etc) — it's the approach that gives the best experience for your visitors.

If all you care about is Android and iPhone user then fair enough.