C#

class GsmNumber
{
    // ..... //

    private int? _CompanyID;
    public int? CompanyID
    {
        get { return _CompanyID; }
        set { _CompanyID = value; }
    }
}

class Company
{
    private int _CompanyID;

    public int CompanyID
    {
        get { return _CompanyID; }
        set { _CompanyID = value; }
    }

    private string _CompanyName;

    public string CompanyName
    {
        get { return _CompanyName; }
        set { _CompanyName = value; }
    }

    public static List<Company> GetCompanyList()
    {
        //  filling  list with  Company objects
        // ........ //
        return new List<Company>();
    }
}

_uiCompany.DisplayMember = "CompanyName";
_uiCompany.ValueMember = "CompanyID";
_uiCompany.DataSource = Firma.GetCompanyList();

GsmNumber oNumber = new GsmNumber();
oNumber.CompanyID = 3;

_uiCompany.DataBindings.Add("SelectedValue", oNumber, "CompanyID");