modem disconnect

This crazy supramax 56k v92 voice modem connects at 49333 to Academic Planet for the first five minutes and surfs like mad. Then as sure as the sun will shine, it disconnects. After the reconnect, It stays connected as long as you want.This is a consistent behavior and modem strings from sonic blue only change the reported connect speed and do not fix the problem. I have updated the driver and tried 4 different modem strings to no avail. HELP!!!