MainActivity.cs

using Android.App;
using Android.Content;
using Android.Net;
using Android.OS;
using Android.Widget;
using Core;

namespace Phoneword
{
    [Activity(Label = "Phoneword", MainLauncher = true, Icon = "@drawable/icon")]
    public class MainActivity : Activity
    {
        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            SetContentView(Resource.Layout.Main);

            var phoneNumberText = FindViewById<EditText>(Resource.Id.PhoneNumberText);
            var translateButton = FindViewById<Button>(Resource.Id.TranslateButton);
            var callButton = FindViewById<Button>(Resource.Id.CallButton);

            callButton.Enabled = false;

            string translatedNumber = string.Empty;

            translateButton.Click += (sender, args) =>
                                     {
                                         translatedNumber = PhonewordTranslator.ToNumber(phoneNumberText.Text);
                                         if (string.IsNullOrWhiteSpace(translatedNumber))
                                         {
                                             callButton.Text = "Call";
                                             callButton.Enabled = false;
                                         }
                                         else
                                         {
                                             callButton.Text = "Call " + translatedNumber;
                                             callButton.Enabled = true;
                                         }
                                     };
            callButton.Click += (sender, e) =>
                                {
                                    var callDialog = new AlertDialog.Builder(this);
                                    callDialog.SetMessage("Call " + translatedNumber + "?");
                                    callDialog.SetNeutralButton("Call",
                                                                delegate
                                                                {
                                                                    var callIntent = new Intent(Intent.ActionCall);
                                                                    callIntent.SetData(Uri.Parse("tel:" + translatedNumber));
                                                                    StartActivity(callIntent);
                                                                });
                                    callDialog.SetNegativeButton("Cancel", delegate { });

                                    callDialog.Show();
                                };
        }
    }
}