在5.0以前的版本，虽然现在使用量比较小了，但是在2年前，在其上面发送短息可以说很是费劲，当时确实还让我头疼了一段时间，需要用户自己封装底层的API，然后进行调用，我这里有一个，贴出来，以供大家参考

using System;
using System.Runtime.InteropServices;
using System.Text;

namespace SmartSMS
{
  /// <summary>
  /// 短信发送程序
  /// </summary>
  public class SMS
  {
  public SMS())
  {
 
  // TODO: 在此处添加构造函数逻辑
  //
  }
  private const string SMS_MSGTYPE_TEXT = "Microsoft Text SMS Protocol";
  private const int SMS_MODE_SEND = 2;

// Open in send mode
  private const int SMSDE_GSM = 2;

// Use standard GSM encoding;
  private const int SMSAT_INTERNATIONAL = 1;

// International number format
  private const int PS_MESSAGE_OPTION_NONE = 0;

// No message options
  private const int PS_MESSAGE_CLASS0 = 0;

// Show but do not store
  private const int PS_MESSAGE_CLASS1 = 1;

// Store and show
  private const int PSRO_NONE = 0;

// No replacements
  private const int SMS_OPTION_DELIVERY_NONE = 0;

// No delivery options
  private const int SMS_MAX_ADDRESS_LENGTH = 256;

// Max length of address

  [DllImport("sms.dll")]
  private static extern int SmsOpen(
  string ptsMessageProtocol,
  int dwMessageModes,
  ref IntPtr psmshHandle,
  int phMessageAvailableEvent);

  [DllImport("sms.dll")]
  private static extern int SmsSendMessage(
  IntPtr smshHandle,
  int psmsaSMSCAddress,
  IntPtr psmsaDestinationAddress,
  int pstValidityPeriod,
  IntPtr pbData,
  int dwDataSize,
  IntPtr pbProviderSpecificData,
  int dwProviderSpecificDataSize,
  int smsdeDataEncoding,
  int dwOptions,
  int psmsmidMessageID);

  [DllImport("sms.dll")]
  private static extern int SmsClose(IntPtr smshHandle);

  [DllImport("coredll.dll")]
  private static extern IntPtr LocalAlloc(uint uFlags, uint uBytes);

  [DllImport("coredll.dll")]
  internal static extern IntPtr LocalFree(IntPtr hMem);
  private static IntPtr AllocHGlobal(IntPtr cb) 
  {
  IntPtr hmem;
  hmem = LocalAlloc(0x40, (uint) cb);
  return hmem;
  }
  private static void FreeHGlobal(IntPtr hglobal)
  {
  LocalFree(hglobal);
  public static int SendSMS(string Number, string Message)
  {
  int returnValue = 0;
  IntPtr smsHandle = new IntPtr(0);

  // Set address structure
  byte[] smsatAddressType = BitConverter.GetBytes(SMSAT_INTERNATIONAL);
  byte[] ptsAddress = Encoding.Unicode.GetBytes(Number);
  byte[] smsAddressTag = new byte[smsatAddressType.Length + ptsAddress.Length];
  Array.Copy(smsatAddressType, 0, smsAddressTag, 0, smsatAddressType.Length);
  Array.Copy(ptsAddress, 0, smsAddressTag, smsatAddressType.Length, ptsAddress.Length);
  IntPtr smsAddress = AllocHGlobal((IntPtr)smsAddressTag.Length);
  Marshal.Copy(smsAddressTag, 0, smsAddress, smsAddressTag.Length);
  // Set provider data structure
  byte[] dwMessageOptions = BitConverter.GetBytes(PS_MESSAGE_OPTION_NONE);
  byte[] psMessageClass = BitConverter.GetBytes(PS_MESSAGE_CLASS1);
  byte[] psReplaceOption = BitConverter.GetBytes(PSRO_NONE);
  byte[] smsProviderDataTag = new byte[dwMessageOptions.Length +
  psMessageClass.Length + psReplaceOption.Length];
  Array.Copy(dwMessageOptions, 0, smsProviderDataTag, 0, dwMessageOptions.Length);
  Array.Copy(psMessageClass, 0, smsProviderDataTag, dwMessageOptions.Length,
  psMessageClass.Length);
  Array.Copy(psReplaceOption, 0, smsProviderDataTag, dwMessageOptions.Length +
  psMessageClass.Length, psReplaceOption.Length);
  IntPtr smsProviderData = AllocHGlobal((IntPtr) smsProviderDataTag.Length);
  Marshal.Copy(smsProviderDataTag, 0, smsProviderData, smsProviderDataTag.Length);
  // Set message
// Encoding unicode = Encoding.Unicode;
// Encoding utf8 = Encoding.ASCII;
// byte[] smsMessageTag1 = Encoding.ASCII.GetBytes(Message);
// byte[] smsMessageTag = Encoding.Convert(utf8,unicode,smsMessageTag1);
  byte[] smsMessageTag = Encoding.Unicode .GetBytes(Message);
  IntPtr smsMessage = AllocHGlobal((IntPtr)smsMessageTag.Length);
  Marshal.Copy(smsMessageTag, 0, smsMessage, smsMessageTag.Length);

  // Get handle
  if (0 != SmsOpen(SMS_MSGTYPE_TEXT, SMS_MODE_SEND, ref smsHandle, 0))
  returnValue = -1; // Could not open
)
  // Send message
  if (0 != SmsSendMessage(smsHandle, 0, smsAddress, 0,
  smsMessage, smsMessageTag.Length,
  smsProviderData, smsProviderDataTag.Length,
  SMSDE_GSM, SMS_OPTION_DELIVERY_NONE, 0))
  returnValue = -2;

  FreeHGlobal(smsMessage);
  FreeHGlobal(smsProviderData);
  FreeHGlobal(smsAddress);

  // Release handle
  if (0 != SmsClose(smsHandle))
  returnValue = -3;

// Could not close

  return returnValue;
  }
  }
}