When i implement the Celltrust SMS gateway API, I face an error like this "206Security violation!!", then I go through the document found the below lines White list your Server The most affective way to secure your account is to limit the number of servers that can use it. This is achieved by registering your server with the CellTrust SMS Gateway. The process for white listing a server is: 1. Login to CellTrust Gateway portal 2. Click on My Gateway and then on Account Module 3. Enter your IP addresses in Server Validation Section. Use comma to separate IP addresses if you need to white list more than one server. After I complete the above steps its working fine. Note: The some server has problems, IP may blocked by some countries.