A friend offers me to buy a nice cell phone. But I don't know what operator I will have yet. Is it possible that the cell phone is only on one? Or do all the operators go to all the phones?
I suspect that since 2002 (or 2003?) Czech operators have not been allowed to block phones only for the use of their "SIM". So if the phone is designed for the Czech market, the SIMs of any operator will work in it. If it was bought "elsewhere", it's hard to say - the legislation is not uniform worldwide. But the easiest way to find out is to try a SIM of at least two operators - if both work, either will work.