EAP-SIM has _not_ been implemented, so its not just UI missing.

And even if you try to recompile N900 libicd-network-wpa, you will notice that javispedros wpasupplicant is compiled without CONFIG_EAP_SIM, so there is no support currently in that way either.

Summa summarum EAP-SIM is not supported and most likely will never be supported, unless you code everything yourself.