It depends on the country but not in general. F.e. in Poland it’s illegal to play poker with cash with your friends but in Czech Republic it is not and LEGAL

Technically no. Oral contract is legally binding contract too. Especially if you have witnesses ( I presume 3+ is enough )

They say so. They always say so :-)

It sounds illegal because if one user opt ins for wire tapping, she / he needs to inform other people on the line about it is being wire tapped.