how do websites like twitter recieve text messages and put them on the site
and is this possible with php? or is it a combo of php and something else

Of course it's possible with PHP!

First, you need to set up an service with a "sms gateway" [ http://www.google.com/search?hl=en&l...y+&btnG=Search ].
They set up their servers, so that when someone sent a SMS to a precise number (ususally with a code in the prefix) the message is tagged for your account.

Then, it's just an connection from your script to their server to catch the message body.
Usually by using SOAP, or XML-RPC...

Google for Ozeki message server.

Connect your mobile phone to your PC, configure Ozeki (which is quite simple), fire up it's web-plugin and any messages that get sent to the mobile, Ozeki sucks them up and fires them off to a URL that you specify.

You can specify parameters in the URL too.

Then all you need to do is put up a PHP/ASP script to handle the request and fire all the info into a MySQL database (or similar).

Then it's just upto your web app to output it as needed.

I have tried this in practice so it's not as theoretical as it sounds. I used Ozeki server to develop an application that used an SMS shortcode before we ported it onto the service provider's own platform.

Nice thing about it is that it can send messages with different keywords to different URLs if you want to. Or it can pick out the keyword and send it as a parameter for your script to deal with.