Hi! It is nice to see your post here. Currently I am working with application such yours. But I am using GSM terminals to send / receive data. So I have my "modems" ready to use.
First receiver / trasmitter is PC, the second is 8052 based controller. To do the transfer using PC is easy, but what about 8052?
I have found a lot of applications how to use i.e. Rockwell chips. But I didn't found how to connect an oridinary PC modem via serial RS232 to the uC system.
In the first step I have tried how software handshake has worked. But I am not quite sure if it was good for my modem. Now I must do hardware handshake and your informations are very usefull to me.
If you want, I can send you schematic which is using RT224ATF chip with complete software. Really very good solutions you can find at iReady web site. Do you know iReady?

Jacek