You get it from 3, either visit their shop or their website. It's a little router basically. It connects to 3G, then shares the connection via ordinary Wifi. So your laptop, iPad and anything else that uses Wifi can get online at the same time using the Mifi device. There are loads of different deals that 3 offer.
That's what I know for definite. Now the following is stuff I still need to find out. Apparently you can get the Mifi unlocked (3 will even do it for a fee). This is true, but I want to use my O2 sim card from my iPhone in the Mifi. I've still to get confirmation that this would actually work.
Sweet, this sounds good! well if i can get it unlocked and use my 02 iphone sim! tho will be anoyin not being able to use my phone.