Public gateways are often referred to as SMSC or SMS centers. The centers typically run a robust software application (like advanced versions of those mentioned above) and subscribe to a large database that allows for the messages to be routed to the appropriate carriers using the appropriate settings. When using an SMSC the sender incurs a per message charge. Cost will vary depending on the SMSC used to send the message but its not uncommon for it to cost .05 per message.