This took me 3+ hours to find out; it took the 3rd or 4th person in tech support, who had to ask someone else themselves.
- Open the MiFi 2200 User Guide that you can access when you first connect the unit to a Windows PC via. the USB cable. The link is under "Documentation".
- On page 22 there is a section called "Login"- it contains the password you need to get in.
For pete's sake, change the password!
Otherwise, you will forget that the curious guy next to you on the plane, who you have kindly given access to for a few moments to your MiFi hotspot (and who knows this password) will log in, change it and lock you out.
Don't know if there is a hard reset capability on this unit, but it's easier to just change the password yourself... and don't make it the security code, either 
FYI