static void Main(string[] args)
{
var MobOperator = new MobileOperator();
var simpleAcc = new MobileAccount(1111111);
MobOperator.AddAccount(simpleAcc); // [1]
MobOperator.CreateNumber(); // [2]
MobOperator.RegisteredAccounts[2].AddFriend(simpleAcc, "Chernytsyn Vladyslav");
MobOperator.CreateNumber();
MobOperator.CreateNumber();
MobOperator.RegisteredAccounts[0].MakeCall(MobOperator.RegisteredAccounts[1]); // simple call
MobOperator.RegisteredAccounts[1].SendSms(MobOperator.RegisteredAccounts[2]); // sms from friend
MobOperator.RegisteredAccounts[1].MakeCall(MobOperator.RegisteredAccounts[2]); // call from friend
Console.ReadLine();
}