This is a very tough, tough question, as both the EA (maker of the game) and Supra (maker of the modem) have yet to provide a solution.
I own a Supra Express 288i PnP and I can make all the calls I want to other opponents when I want to play, but I can't receive any. For some reason, when someone calls me, we always get hung up on the verification (which is the handshake negotiation). EA Sports told me that I needed to turn the compression off - %C0 -, disable the flow control - &K -, and disable the error correction - &M0 -, by doing this, my modem would be able to negotiate the handshake and we would connect, thus I created an initialization string of AT&F%C0&K&M0 but had no luck with this either. I have also used basic init. strings, such as AT&F, the generic settings, as well as the preset (Supra settings) and none of them work in regards to receiving calls. Yet, I can receive calls from another Supra modem, without any problems, so receiving calls does work.
Finally, My modem is a SupraExpress 288i PnP at 28.8 speed.
In essence, my question is: "How do I get my Supra Modem to receive calls from non-Supra Modems"?