SMS to website posting system

I am in need of some help from a coder who has worked with SMS Gateways within websites/Apps before.

I need a script that I can insert into my website, which will

1) Allow mobile users to send an SMS which appears on my website
2) Allow web users to send a reply to the text message

I am making the site, but need help setting up the SMS Gateway and converting the text-messages to PHP to have them appear on the site.

I will of course cover the cost of the SMS Gateway and text message bundle. I have looked at a few, but am happy to go with the advice of the freelancer with regards to which provider to use. Ideally one that charges less than 4p per message.

Tech spec:
This should be quite a simple task for someone who has done this before. There will be no styling necessary, just the HTML to display the text messages in a legible way.

Text messages should display with, ideally
Date and time
The 'from' Number
Message body

Then a 'reply' button underneath

The reply button should store the outgoing number and include a text box for the reply. Plus a 'send' button

Deliverables to me should include
- A detailed discussion and test-through of the code
- All files including HTML, PHP and any XML/Java which is used. I am not picky about the method.

Please contact me if you have any questions

Thanks!