There is a python script which does exactly what our client is looking for. It uses the g-calendar SMS notification for sending messages to the g-accounts user.
You can find the python script at: http://www.kryogenix.org/code/send_sms_via_gcal.py.txt

We need a solution which runs as PHP script without python requirements or others.

There is a gdata-library for PHP, too: http://framework.zend.com/download/gdata

You need to set up your gcalendar to send such messages etc. Do so and make sure You are aware of this task BEFORE bidding!!!

We will tell the ISP to give a SSH and S/FTP account at a Apache/PHP server for You for testing.

The job must be completed within 5 days because client's contract is limited to this time period. Delivery after that is not accepted. Once You are done, we can pay and receive the script files by email.