I hope this gets a response.
Say Person A sends an SMS to a shortcode in a certain syntax. How could a confirmation SMS be sent to Person A's mobile phone automatically ("Your message has been received successfully!"), after determining that the SMS received from Person A is in the correct syntax? I'm a total newbie when it comes to SMS - so if anyone could describe the entire end-to-end process/architecture that could make this happen, I'd be grateful!
You'd have to find a gateway provider who handles the receiving and the sending of messages for you using a defined API talking to a script/application in the language of your choice.
You usually receive messages on a number defined by the gateway provider. Incoming messages will trigger a call to a URL defined by you. Behind that URL will usually be a script that then performs the desired actions (e.g. parsing the message and sending an automated response SMS through the gateway provider.)
SO questions related to SMS Gateways:
BulkSMS provides facilities for you to both send mobile terminating (MT) messages and handle receipt of mobile originating (MO) messages.
You can request a short code, which your users then send MOs to. The message can then be relayed, via a simple HTTP request, to your web server. You application then determines a suitable response and replies via SMS by calling the MT API of BulkSMS.
There may be restrictions and legislation applicable, depending on where you are, where your users are and the networks the messages are passing through. They can provide assistance here too.
International incoming numbers http://www.bulksms.com/int/w/solutions_incoming.htm
Receiving messages via HTTP http://www.bulksms.com/int/docs/eapi/reception/http_push/
Sending API http://www.bulksms.com/int/docs/eapi/
Short codes in South Africa http://bulksms.2way.co.za/w/solutions_psms.htm
Hope this helps