They optimize the webpages for mobile phones by stripping them of all unnecessary HTML tags, embeds and formatting styles.
The next question - do you need to know about these services if you access the web only from a desktop computer ? Well, the answer is yes and here are some reasons:
For users on a slow internet connection (like a dial-up)
Dial-up users will probably feel more productive when they browse the web via these services as the page loads will happen much faster.
While Google Mobile and Mowser will divide a webpage over several pages, Phonify will present everything on one page so it's more suitable for browsing on desktop computers.
How Search Engines see my site ?
Though Google Cache is a good tool to understand how web crawlers look at your site, Phonifier is another great option since it generates a very clean view of your webpage as it appears to the search engine bots. [Thanks John]
Create a Mobile version of your Blog
Don't have the time to create a mobile friendly version of your website. No problem - ask the mobile phone and PDA users to browse your site via Phonify or Mowser.
They'll love the experience. See real examples on Mowser, Google Mobile and Phonifer.com. You can toggle the display of images in Mowser and Phonify.
As a proxy to open restricted websites
You may access blocked websites in your school or work by using Google Mobile or any of the other two services as a proxy.
Since the browser request is sent via Google.com, the internet filters will normally not block the page.
For example, to access the Myspace profile of Madonna, type the following address in your web browser and the page is very likely to open on your school computer without problems:
More: PHONifier is an open source project that anyone can download free of charge. You could install the PHONifier script on your server to have it automatically update your webpages when a mobile device tries to access them.