Please check sub-table 2 for the operators corresponding to different countries, please update the operation according to your site. For example Germany is: T-Mobile, Vodafone, E-Plus E-+ Mobilfunk 

1.I’m sure it’s glass - when I clean mine with isopropyl alcohol they make that ‘squeaky’ noise you get with glass rather than plastic, and they’re more resistant to scratches than most plastics are. According to manufacturer website K & F use German optical quality glass so I’m sure they would have been called out for that a while ago if it wasn’t true 2.I drop one last year and it broke like glass ..I’ve found them easy to clean and well made. 3.Looks and sounds like glass to me 4.HD optical glass 5.As far as I can tell it is glass. Excellent optical qualities 

Hi, I'm pretty sure the dimensions of the S21 you state are no bigger than my iPhone 13 Pro Max? Given this being correct, it will fit and operate okay. As a footnote, the X2 is excellent and works terrifically well... 

From my opinion the answer is no ! mine it’s a 82 mm and there no way to hook a Lens cap on it 

I am pretty sure any smart phone will work with this monocular. We have not yet gone SMART but intend to. Good luck if you buy , it’s great