I've been looking at systems such as txtlocal, esendex and clickatell. I need to send out a very large number of messages and ideally would like to go in at a lower level then using systems like these. Does anyone know how these SMS gateways like I've listed work in terms of actually sending out the messages? Will they have agreements with different carriers and be sending them out programmatically? I've tried contacting some UK carriers directly but as of yet haven't had any success getting any information from them.