我的GetPhoneNumber()对不对??

[gundumw100]

[DllImport("sms.dll")]
private static extern IntPtr SmsGetPhoneNumber(IntPtr psmsaAddress);//检索 SIM 所有者的电话号码

public static unsafe string GetPhoneNumber()
{
Byte[] buffer = new Byte[516];
fixed (byte* pAddr = buffer)
{
IntPtr res = SmsGetPhoneNumber((IntPtr)pAddr);
if (res != IntPtr.Zero)
throw new Exception("无法从 SIM 中获取电话号码");
}
string PhoneNumber = Encoding.ASCII.GetString(buffer);
return PhoneNumber;

}
//PhoneNumber就是我得到的电话号码了????????