I found a way, but cannot realize it at all. Here is what I found:
I connect the modems by "line" port. I use AT command ATD to connect the client to the server. This command makes the modem dial, without waiting for a signal. In the other side a must make the server modem to answer without waiting for a ring. This can be done by ATA command. The problem is that I cannot figure out how to initialize the server modem with this command. I connected them in this way only via Hyper Terminal, but it doesn't works for me.