https://answers.microsoft.com/en-us/mobiledevices/forum/mdlumia-mdtips/lumia-640-xl-lte-model-variants/e6712e54-c6b5-466f-a731-358901cc1fd1
this link shows details of variations of 640 xl phones
What is the difference between rm 1067 and rm 1096 in regards to microsoft phones