Broken back, glass panel
I am with FIDO a GSM provider in Canada. Your info says the glass back works on an iPhone 4 (GSM/AT&T). Will it work on my GSM/FIDO phone?
It sure will! The only difference with GSM/AT&T and GSM/FIDO is the service provider.
GSM - Global System for Mobile Communications
AT&T - Service provider
It does not matter which service provider you are with, as long as your iPhone is GSM compatible.
So in short, if you have a GSM iPhone with a GSM part, it will be compatible.
However if you have a CDMA iPhone with a GSM part, it will NOT be compatible and vice versa.
Hope this helps!