Arduino Uno + sim900

hi i am trying to make a call or send an sms using this combination of uno and sim900

well i am using a IComSat v1.0 sim900 and arduino 1.0 to program
http://iteadstudio.com/store/images/produce/Shield/IComSat/icomsat_DS1.2.pdf
thts the datasheet...

but everytime i try to upload my program to the uno the sim900 stops responding. and then dsnt turn on.

//Serial Relay - Arduino will patch a 
//serial link between the computer and the GPRS Shield
//at 19200 bps 8-N-1
//Computer is connected to Hardware UART
//GPRS Shield is connected to the Software UART 
 
#include <SoftwareSerial.h>
 
SoftwareSerial mySerial(7, 8 );
 
void setup()
{
  mySerial.begin(19200);               // the GPRS baud rate   
  Serial.begin(19200);                 // the GPRS baud rate   
}
 
void loop()
{
  if (mySerial.available())
    Serial.write(mySerial.read());
  if (Serial.available())
    mySerial.write(Serial.read());  
 
}

the program is to allow a connection and then let me use at commands to make calls or send sms but it seems to not work.

if there is a easier program please let me know
thx.

Read the part of the data sheet about data consumption.

The board / chip can draw anywhere between 500 and 2000mA. Make sure your external supply is capable of providing that much current, since USB won't be able to.