There is AQL , Intellisoftware and the most famous of most Clickatell gateways , which either provide PHP samples or simple interfaces (such as Soap, XML, etc.). When you receive an SMS message, most systems either call your server (i.e., via Soap / XML with a complete message with the URL you specified, or with a message identifier, which you can then request on your server for complete information about message: some also if necessary, give "email" notifications.
I used one of them quite successfully a few years ago, but it doesn't seem to work anymore.
see also Receive SMS messages using a web application .