For me I had one bar coverage in mobile when outside, but zero when inside. As SXT has a directional antenna, so the gain is higher, even a tiny signal can get you good speeds, if mounted externally. I haven't found a single person who was technical enough to answer from Three tech support in last 8 years. Having said that, they are the only ones who are doing truly unlimited data for less than £20. Just you need to make sure that you are getting some sort of Three signal in band 3 (can be checked on mobile app).