arduino uno + ethernet shild + sim 900 GSM shild - will be possible?

Hi,

I want to build a small project to send sms from php scripts from centos server via http ( or other protocot) to arduino uno with ethernet shild + sim 900 GSM shild.
I want to transmit from PHP script also the sms message to arduino for delivery.

will be that possible? how should i start this? any guidance?

thank you

Look at the shields to see if they do or do not share pins .
Get one working first , then the second .