How to manage multiple phone lines at the same time

using System;
using System.Threading;
using Ozeki.VoIP;

namespace Multiple_phone_lines
{
    class Program
    {
        static ISoftPhone softphone;   // softphone object
        static IPhoneLine phoneLine;   // phoneline object
        static IPhoneLine phoneLineTwo;  // second phoneline object

        private static void Main(string[] args)
        {
            // Create a softphone object with RTP port range 5000-10000
            softphone = SoftPhoneFactory.CreateSoftPhone(5000, 10000);

            // SIP account registration data, (supplied by your VoIP service provider)
            var registrationRequired = true;
            var userName = "858";
            var displayName = "858";
            var authenticationId = "858";
            var registerPassword = "858";
            var domainHost = "192.168.115.100";
            var domainPort = 5060;

            // Second SIP account registration data, (supplied by your VoIP service provider)    
            var registrationRequiredTwo = true;
            var authenticationIdTwo = "859";
            var userNameTwo = "859";
            var displayNameTwo = "859";
            var registerPasswordTwo = "859";
            var domainHostTwo = "192.168.115.100";
            var domainPortTwo = 5060;

            var account = new SIPAccount(registrationRequired, displayName, userName, authenticationId, registerPassword, domainHost, domainPort);
            var accountTwo = new SIPAccount(registrationRequiredTwo, displayNameTwo, userNameTwo, authenticationIdTwo, registerPasswordTwo, domainHostTwo, domainPortTwo);

            // Send SIP regitration request
            RegisterAccount(phoneLine, account);
            RegisterAccount(phoneLineTwo, accountTwo);

            // Prevents the termination of the application
            while (true) Thread.Sleep(50);
        }

        static void RegisterAccount(IPhoneLine phoneLine, SIPAccount account)
        {
            try
            {
                phoneLine = softphone.CreatePhoneLine(account);
                phoneLine.RegistrationStateChanged += line_RegStateChanged;
                softphone.RegisterPhoneLine(phoneLine);
            }
            catch (Exception ex)
            {
                Console.WriteLine("Error during SIP registration: " + ex);
            }
        }

        static void line_RegStateChanged(object sender, RegistrationStateChangedArgs e)
        {
            if (e.State == RegState.NotRegistered || e.State == RegState.Error)
                Console.WriteLine("Registration failed!");

            if (e.State == RegState.RegistrationSucceeded)
            {
                Console.WriteLine("Registration succeeded - Online!");
            }
        }
    }
}

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