Can Oracle RBBMS communicate via modem

This depends a lot on the parameters of the data transfer and communication. Eg is it something that happens at a regular interval, or is it triggered by changes in one database, and is it one way or bi-directional?

A simple way may be to use a shell script running from crontab to execute a small PL/SQL query, and based on the results, initiate a data extract to file, then dial the modem and perform the file transfer. The server at the other end could have another crontab script that looksfor the received file, and when found, uses SQL*loader or similar to update that database. This is assuming a fairly small amount of data is involved. It also requires the destination modem to be configured for auto-answer which is not secure. Not sure whether fixed number dial-back could be implemented this way.

Never done this so it's just a guess.

HTH
William

Set up a dial-up connection between the machines which runs PPP. The two machines will think they are on a (very slow) wan, and should transfer data just fine. You will probably need to set routes up to make this work seamlessly. You may also have to increase default time-outs.

Good luck.