iPhone 6 Model A1549 problem

Hi to all! I just want to ask for a clear explanation of this unexpected thing happen with my iphone 6 model A1549. I purchased iPhone 6 model A1549, an open line unit. I travel back here in the Philippines using my purchased iPhone 6. I used sim card (GLOBE) in my iPhone 6 and found it works. My problem now, though my iphone 6 model is not supported model for the philippines which is supposed to be the model A1586. Why my phone can still detect Globe Networks though the signal always changed from 3G to LTE then LTE to 3G. Also my signal always dropped. Can someone help me to understand the use of frequencies per iphone model which is dedicated only for each countries.