nokia phone 5110 plug-in

I am trying to develop a short messages service (sms) autoresponse database using filemaker pro6 and a nokia cellphone 5110 and a pc suite serial communication port connector (DB9 connector). What this database do is that it will receive short messages service (SMS) text from an account/member and it will automatically respond to the cellphone where the message originated. All the short messages service (sms) text received are inquiry for a balance account. My problem started on how to send back an inquiry response to where the inquiry originated. I wud like you to know that i already checked the troi plug-in and its very cool however the problem is how to let the nokia 5110 cellphone know when to send/receive the sms, because though the troi plug-in lets you listen/receive data from the serial/comm port, the send/receive method needs an interface for the cellfone to send/receive it from/to requester. I search the entire forum and i cannot find one that even mentions sms or cellphone. can anyone help me on this. I hope there is a plug in somewhere which can address this issue.