So, I recently had same problem as everyone else > 3g red light flashing.  I reset both my router and modem and unplugged microcell.  For 24 hours after doing this, it worked.  Now, the 3g red light flash is back and NO MCELL!  My router is the Cisco E4200 and Modem is the Actiontech MI424.  I changed the MTU as referenced on line in an attempt to fix the problem.  No dice.  Is there a solution?  Or do I now own a door stop?

FWIW: I also am using the VZ network extender in my house as we are on VZ as well as at&t.  The VZ NW extender works and has worked from the begining.  So, I am no expert but the problem seems to be with Microcell.