I've just release V0.6 of the uNetSerial internet processor chip at
formatting link
.There is a free version that runs on the Mega128 and has been tested with many ISP's dialed up with a modem and several GPRS phones. It also comes with a windows emulator so you can test without an embedded platform.
With a few simple serial commands you can communicate over the internet via GPRS or dialup.
Burn this code in your Mega128 and give it a try!
Thanx,
Mike