If you want to pay someone to write the code for you, you need to be over at Gigs and Collaborations. Otherwise please post the code you have along with details of the hardware you are using and how it is connected together.
In this rare instance ignore what PaulS has written, you are writing to the different serial ports correctly on the assumption you are using a Mega.
Having had a play you are filling up your buffer with the responses from the AT commands issued in Sim900_Inti(). Don't forget non visible characters. Then it appends what it can from your message which is what you see.