I can recall a few years back a gentlemen running a Blackberry Storm on T-Mobile’s network and I was like ???  But those were the days when global phones on Verizon’s network wasn’t as widespread as they are today.  I quickly learned that the device was a global device and could be used to roam on GSM networks (dual-sim slot) outside of the U.S.  Devices like that were important for businessmen and woman requiring a smartphone that could operate nearly everywhere they traveled.  Well, global devices are becoming more of the norm on Verizon’s network and so it’s no surprise anymore to see a Verizon branded “Droid” on a GSM carrier like T-Mobile or AT&T.  So what do you need to make it work?  For starters, you’ll need a Motorola Droid 4, Bionic or Razr on Verizon and a few top notch guys from everyone’s famous and favorite site, XDA Developers.  Because these devices support global GSM bands, a little bit of tinkering and few modifications, one can be all set to run on the GSM carrier of their choice.  This is in part due to the fact that the device’s MDM6600 radio is compatible with AT&T’s HSPA technology and T-Mobile’s Edge network.  User P3Droid even posted pics over on his Twitter page for proof (pics above and below).  And while this might not be Verizon’s first choice as a means of using hardware ultimately designed to work on their network, tough stuff Vz, this is how Android users do it.  The dev’s have been presented with some challenges due to the locked bootloaders issue, but you know XDA, they always come through.

source: XDA