modem communication with Unix<->PC

I am doing some data syncronization between a database running on PC with Powerbuilder and a database running on UNIX Informix. I have all of the syncronization issues covered but my problem is the transfer of information between PC and UNIX. I want to be able to press a button on my Powerbuilder app. and internally have the modem dial up the UNIX and transfer some ascii file back and forth. I have access to PC x,y,z modem libraries but the UNIX end is posing a problem. Does anyone know of a way to deal with this issue? Perhaps a 3rd party library (preferably that can run in the background)? Please e-mail me a copy of your post. -pjk