In order to convert AMR files to MP3 files, you will need to purchase an audio converter. There are several free ones online and available for download.
The easiest way to convert your files to mp3 is to download a file converter off of the internet. I found a great converter at www.maniactools.com/soft/m4a-to-mp3-converter.
Try www.convertit.com
Audacity is a program that allows you to record and edit sound files. Additionally, the Youtube Downloader is able to convert files from .wav to .mp3, and even convert video files into sound.
http://myrightbrain.wordpress.com/2006/06/11/how-to-convert-mp4-audio-files-to-mp3-using-itunes/ There, follow the instructions and convert it. Or you could look at some programs.
CNet has a free software that allows users to convert FLAC files to MP3 files, whether for use on an iPod or on iTunes. The free converter can be downloaded on CNet.
Short answer is you cant. Think of an mp3 as a recorded act of music, and a midi as a piece of sheet music. The only way to convert would be to listen to the mp3, and create a midi from what you hear. There are things called pitchriders that can convert a simple sound like a single guitar string or a note from a clarinet into a midi note number, but these are simple waveforms. An mp3 recording of a song is a very complex waveform which would confuse a pitchrider.
You can convert wav files to mp3 files using iTunes. In iTunes, select Preferences then Importing Settings then Import Using. Then click the advanced menu and click "Create mp3 version."
There is a cool software called "mp3 cutter joiner" in which you can convert .wav to .mp3. It says that it's a cutting and joing program but you can use it as a converter and also a bitrate cutter.
In iTunes Right Click on an MP3 file listed in the Library and select Convert to AAC from the menu that appears.
BUY mixcraft
I think you can convert .oma files to .mp3 format file with format factory.it is available on http//www. softpedia.com