What is a Mifi card? How can you use your smartphone as a wireless hotspot?

I have owned a  MiFi card and I have used my blackberry as a hotspot.  A MiFi Card allows a user to connect a device with wireless to the Verizon network.  It basically works as a mobile hotspot for where ever you are as long as you are on their network.  You can use many smartphones these days as a wireless hotspot as well.  The phones connect to your wireless device and acts as a wireless router of sorts, allowing the secondary device to feed off of its signal.  I think the precursor to this was the technology where you could connect your laptop or wireless device to your Blackberry (or other device) via a cable and access data transmitted through the blackberry.  This service preserved my sanity while on 16-hour long EMS tours!