I am not familiar with your equipment. I will list a link for a GSM modem with built in GSM by Entertron. It connects via GSM to www to a PC. On the info page is a link to their manual which may be of some help.
If you are actually building this, and don't have the parts yet, their modem may be a good choice. If you don't have a PLC either, contact them and tell them that you are a student.
"Entertron Site Link"
"Entertron GSM Modem Link"
It appears that you are s student.
If possible, could you answer a few questions for me?
What country are you located in?
What type of class is this for, Electrical Engineering, PLC Programming, or ?
Did you pick out this project, or was it assigned?
Do you actually have to build it?
Does it actually have to work?
Do you have to pay for it?
Did you have any instruction on GSM and modems?
Did you have enough instruction to program the PLC without help?
Did you have any instruction in drawing the schematic?
Thank You.
regards.....casey