convert and combine GSM codec to MP3

Like the title said, I want to combine two audio files with GSM codec to one MP3 file. This is recordings where it is one file for outgoing audio, and one file for incoming audio. They need to be combined into one MP3, keeping the synchronization and the file name: The server is a dedicated Centos 5 minimum Example: [login to view URL] and [login to view URL] wil be: [login to view URL] The best solution for me is that the script will convert the files as soon they are stored, but a script that will run every 5 minutes for example are good too.