hi there,
I did some simple sketch
#include <SoftwareSerial.h>
SoftwareSerial GPRS(7, 8);
unsigned char buffer[64]; // buffer array for data receive over serial port
int count=0; // counter for buffer array
void setup()
{
GPRS.begin(19200);
Serial.begin(19200);
}
void loop()
{
if (GPRS.available())
{
while(GPRS.available())
{
buffer[count++]=GPRS.read();
if(count == 64)break;
}
Serial.write(buffer,count);
clearBufferArray();
count = 0;
}
if (Serial.available())
GPRS.write(Serial.read());
}
void clearBufferArray()
{
for (int i=0; i<count;i++)
{
buffer[i]=NULL;
}
}
and sometimes it works and sometimes not 
when it works, I see sms/call replay and when not, I see some dots (jpeg)
I plug/unplug, curse, wait and sometimes it start working
any idea where this random behaviour come from? (wrong shield??)
