If your GPRS is going in and out like a sine wave, that means you have a problem with the GPRS access at your phone level, and unfortunately this is not a GPRS, Airtel, or Sony Ericsson forum. If it's a bluetooth connection instability, you could try moving the phone closer to the computer, plugging the laptop into power, plugging the phone into power, moving the bluetooth dongle to another USB port, checking if the connection works better on another computer, etc.