press control-shift-o, quite tricky, then close keyboard..portrait mode wont work with keyboard open
when u r browsing the internet only
Web browser has a built in portrait mode without the need of Ctrl+Shift+O (actually, that doens't work anymore). Click on web, click on the main title ("Web") and click on Options -> Settings.
There's an Auto Rotate option. Toggle it and you're done.
The phone itself has portrait mode on some applications, but you have to enable it using Control + Shift + R.
Not every application looks good in portrait (e.g. the media player)