Sadly, Google currently allows only one Google calendar to be synced with a Windows Phone 7 device. This is not the case for Android and iPhone. However, we can trick Google into allowing multiple calendars to be synced on Windows Phone 7 running Mango.

I was looking for a simplest solution which led me to the article which clearly explains the process . The issue I had with the instructions was the requirement of having Safari browser installed in order to set the browser user agent to impersonate iPhone. I had no intention of installing Safari. I was determined to use Firefox which I already had installed. I was interested in setting the user agent from Firefox. User Agent Switcher, the Firefox add-on, allows users to switch to iPhone user agent so that websites are tricked into believing that the browser visiting the site is Safari for iPhone. Once the add-on has been installed, we need to got to Firefox Tools->Default User Agent and select the iPhone option. The last step of browser configuration involves disabling JavaScript by going to Tools->Options->Content (tab)->Enable JavaScript. At this point Firefox is ready to be used to enable multiple Google calendars. Go back to the instructions article referenced above to complete the process.

Message to Google: Please do not discriminate against Windows Phone 7!