I do not think you're going to be able to do that. There might be some legacy infrared machines that are able to see the E71 and configure it as an analogue modem, but I think you are going to be generally out of luck.
But...why not use packet data? Even at EDGE speeds, even with a slightly increased latency, you're still going to beat dial up.
Are you trying to use the phone to dial into a server's emergency modem or something?