Convert uploaded mp3 to gsm on the server (Or other 8 bit file type)

We need a way to allow a user to upload an MP3 or WAV and then process it like so: - Determine audio clip length in seconds. (If not possible, then just the file size) - Trim the clip down to X seconds - Save the file off once as an mp3 (or preferred web-playable file type) - Convert to GSM or similar format for usage in a PBX/Asterisk system. We'll also look for your expertise on what file format to save into and which Codec to use for serving up the audio files on our Phone system. We currently use ulaw and gsm -- we want to get the best quality sound clips and then just understand what resources that requires from the server. We have a system set up to work on already. (openpbx/asterisk/phpagi)