Browse Mobile Websites From Desktop/Laptop
Solution 1:
You can download the firefox plugin User Agent Switcher. This will allow you to spoof any user agent you please. You can choose a user agent from this page. If you wanted to appear to be using an iPhone, you could enter something like this:
Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543a Safari/419.3
Solution 2:
You can use an emulator, to emulate a mobile device.
For example from Microsoft or Android