User blog comment:Suparockr/List of Plotholes throughout the series/@comment-2249774-20120723213353/@comment-1221773-20120725011918

Not a plot hole. Since we don't know what the communicator requires to function (or even if its systems are contained within the armor and not a separate earpiece or implant), it's entirely possible that it could still function after Shepard's armor was damaged.