How do you jailbreak a motorola blur phone?

To give an exact answer you would need to specify what model of Motorola Blur phone. Blur is simply a piece of software in the phone which brings all of your social networking sites such as Twitter, Facebook and MySpace, and syncs them to make one app. This then eliminates the need for multiple logins. Every phone has a different method of jailbreaking, or in the case of android phones, rooting. The best places to look for advice on how to jailbreak your Motorola is YouTube. On here you can find many different tutorial videos for all different types of Motorola phone, most being easy and simple to follow.
Jailbreaking is a term used to describe the process of unlocking your phone to force it to accept third party applications and software. This is not the same as SIM unlocking as unlocking the SIM simply involves allowing the phone to accept a SIM card from any network. If you own an Android phone then you may want to search under the term rooting as this has the same meaning as jailbreaking but applies to android phones only. 
For iPhone users there are multiple sites dedicated to jailbreaking your phone, one of the most popular ones is Ultrasnow, which is full of tips for jailbreaking the Apple phones and iPad.
In many countries, jailbreaking is legal including America and the EU but this process could void any warranty on your phone.