代碼如下:

#region 免費發送飛們接口(2014-01-06 16:20測試有效) 
/// <summary> 
/// 免費發送飛們接口（要開通飛信把對方加為好友才能發，也可以給自己發做測試） 
/// </summary> 
/// <param name="sendNumber">登陸飛信手機號</param> 
/// <param name="sendPassword">登陸密碼</param> 
/// <param name="receiveNumber">接收手機</param> 
/// <param name="Content">短信內容</param> 
/// <returns></returns> 
public bool sendfetion(string sendNumber, string sendPassword, string receiveNumber, string Content) 
{ 

string url = string.Format("https://quanapi.sinaapp.com/fetion.php?u={0}&p={1}&to={2}&m={3}", sendNumber, sendPassword, receiveNumber, HttpUtility.UrlEncode(Content)); 
string strRet = ""; 
try 
{ 
HttpWebRequest hr = (HttpWebRequest)WebRequest.Create(url); 
hr.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)"; 
hr.Method = "GET"; 
hr.Timeout = 30 * 60 * 1000; 
WebResponse hs = hr.GetResponse(); 
Stream sr = hs.GetResponseStream(); 
StreamReader ser = new StreamReader(sr, Encoding.Default); 
strRet = ser.ReadToEnd(); 
} 
catch (Exception er) 
{ 
strRet = ""; 
} 
if (!strRet.Contains(":0")) return false;//成功時返回數據：{"result":0,"message":"\u53d1\u9001\u6210\u529f"} 
return true; 
} 
#endregion 

接口是搭建在SinaAppEngine上的，SAE的服務還算是比較牢靠的。 
發送者用戶、密碼不要寫錯，然后接收者必須是自己或者飛信好友，才能發送成功。