interface IConnectionService
{
    List<TargetDevice> FindDevices();
    void Connect(TargetDevice targetDevice);
    void Disconnect();
    byte[] Read();
    void Write(byte[] command);
}

public interface IMvxPhoneCallTask
{
    void MakePhoneCall(string name, string number);
}

protected void MakePhoneCall(string name, string number)
    {
        var task = this.GetService<IMvxPhoneCallTask>();
        task.MakePhoneCall(name, number);
    }

RegisterServiceType<IMvxPhoneCallTask, MvxPhoneCallTask>();

public class MvxPhoneCallTask : MvxWindowsPhoneTask, IMvxPhoneCallTask
{
    #region IMvxPhoneCallTask Members

    public void MakePhoneCall(string name, string number)
    {
        var pct = new PhoneCallTask {DisplayName = name, PhoneNumber = number};
        DoWithInvalidOperationProtection(pct.Show);
    }

    #endregion
}

public class MvxPhoneCallTask : MvxAndroidTask, IMvxPhoneCallTask
{
    #region IMvxPhoneCallTask Members

    public void MakePhoneCall(string name, string number)
    {
        var phoneNumber = PhoneNumberUtils.FormatNumber(number);
        var newIntent = new Intent(Intent.ActionDial, Uri.Parse("tel:" + phoneNumber));
        StartActivity(newIntent);
    }


    #endregion
}

public class MvxPhoneCallTask : MvxTouchTask, IMvxPhoneCallTask
{
    #region IMvxPhoneCallTask Members

    public void MakePhoneCall(string name, string number)
    {
        var url = new NSUrl("tel:" + number);
        DoUrlOpen(url);
    }

    #endregion
}