Serial Connection of a Sim900 module(not shield)

I have read similar topics of mine but could not find the right answer yet.The module(not shield) site is http://www.elektrovadi.com/GSMGPRS-MODEM,PR-1373.html .I do not want to burn sim900 module with 5 volt coming from arduino uno soft.serial pins(2,3) because the sim900 manual says it uses 2.8VDC. The sim900 module has MCU socket on it which has rx,tx,cts,rts,pwrkey,reset,gnd,Vcc pins. The MCU socket rx and tx pins are directly connected to the sim900's rx tx. There is also an Max 3232 integrated circuit for communicate with PC. My question is if I connect 5V from the arduino to Vcc pin of MCU on Sim900 module, can I communicate with the rx tx cable. I need an advice. What is the right way for communication? Thank you.

I think nobody wants to reply, let me help the others with the solution.
I sent an email to the Simcom company for the problem, I didn’t think they would reply but they did. The reply is below.

"Dear Sir,
This is Jack from SIMCom;for the best performance,you should add some level shifter between them,then could work smoothly.

Thanks
Jack Sun(???)"

The circuit examples they sent is attached.

Hello Guys,

i have a SIM900 on PIN 2/3 (softwareserial) now i have other device on PIN11/12 (PortTwo, Software Serial) >Arduion Uno

Code: PortTwo.listen(); //11/12 >that works!!
But the SIM900 dosen't work. How i can make a "listen()" on this port?

Do I need to adjust the *.h and *cpp files?

Thanks

Andy

I am doing the same thing as the first poster but I was hoping to power both the sim900 and the atmega328 with 4v will the serial work with 4 volts or will it only work with 2.8