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!