I believe you mean "100% of inhabited Poland", and even then you may be wrong. Check this map: https://www.nperf.com/en/map/PL/-/-/signal/ https://www.nperf.com

I believe you mean "100% of inhabited Poland", and even then you may be wrong. Check this map: https://www.nperf.com/en/map/PL/-/-/signal/ https://www.nperf.com/en/map/PL/-/-/signal/ - there are plenty of spaces with gray "no coverage" dots for every operator. The problem is when you have bad GSM coverage in some unfortunate spot even in a big city - you may just can't solve it. And, by the way, there's a habit to place utility meters in basements, where GSM coverage is much worse.