play AVI on my mobile

An AVI file could contain almost any video format (codec). It is practically impossible to create a player for a phone or even a PC that could anticipate every possibility.

However, there is a relatively small set of codecs that are in common use for AVI files. DivX Player on your PC can play most AVI files. Unfortunately, phones simply aren't powerful enough to accomplish the same feat. Phones rely on specialized hardware to decode video and that hardware is limited just a few codecs. For example a DivX certified phone still cannot play as much as DivX PC Player.

Using software, you can often add support for more codecs but since it is software, the size of the videos you can play will be limited and the drain on your battery will be noticeable. You don't notice this on your computer because it has a very fast processor and it's plugged into the wall.

On a phone your choices are, hardware that efficiently handles a few codecs or software that burns through your battery and still can't play large files.

Currently, the best solution is to use hardware and rely on your computer to convert incompatible videos into a format that works on your phone. As hardware improves, the need for conversion will drop. As more DivX Certified phones become available, software like DivX Mobile Player will become obsolete.