While most people have been getting excited about the pre-announcement of Opera Mobile 9.5, the hugely popular (and free) little sister, Opera Mini 4, has just had a big back-end (i.e. the bit that does the work) upgrade, which (among other changes, listed below) should improve browsing speed by (up to) another 20%.

Opera Mini 4 is, as always, at mini.opera.com (from your smartphone).

Changes made this week include, according to the Opera blog post:

• Added a simple UI to the server-side preferences that exists. Go to 'opera:config' to configure some settings.
  
• Tweaked phonenumber detection, there should be somewhat fewer false positives now, but you can now also disable the feature on the opera:config page.
  
• Increased the default timeouts to 40 seconds from 20.
  
• Updated to a HTML rendering engine to be similar to the latest Opera 9.5 weekly release.
  
• Fixed support for entering hostnames starting with a number (eg, 360.yahoo.com) as a URL without the starting http://
  
• Made content folds visible even when the background is black.
  
• Fixed inter-page links ().
  
• Fixed clipping rectangle for iframes with hidden overflow css properties, this bug caused some links inside some iframes to be unclickable.
  
• Fixed HTTP basic auth for pages with non-7bit authentication realm.
  
• Pages with nested <a> tags are now somewhat easier to navigate (<a href='link'>Link 1 <a href='link2'> Link 2</a></a>), it's now possible to follow both the inner and the outer link.
  
• New WML stylesheet.
  
• Various optimizations resulting in the average transcoding time to be 20% lower.