The SIM card is a smart card, i.e. a secure piece of hardware, that protects the telephone network from the subscriber - most importantly, it ensures that the network has someone to bill.
In most western countries, SIMs do little else; however, they are full application platforms, allowing stuff like Kenya's mobile payment network https://en.wikipedia.org/wiki/M-Pesa.
For what it's worth, you really don't want to have every network provider negotiate with Samsung for the particular access policy of that network. "Not compatible with your telephone" indeed!
In most western countries, SIMs do little else; however, they are full application platforms, allowing stuff like Kenya's mobile payment network https://en.wikipedia.org/wiki/M-Pesa.
For what it's worth, you really don't want to have every network provider negotiate with Samsung for the particular access policy of that network. "Not compatible with your telephone" indeed!