Android - What can I do retrieving the serial number of an Android phone?

You can get all the device information using:

android.os.Build.<OPTIONS>

e.g.

android.os.Build.SERIAL

This IMEI number can be use for unique purposes.you can use the IMEI number as unique number for different task.simple example using this number you can verify phone user.

IMEI is an unique identifier for any device. Please look up what IMEI si and what it could be used for.

http://en.wikipedia.org/wiki/International_Mobile_Station_Equipment_Identity

As far as my personal experience goes with how i use IMEI, i use it to uniquely locate and identify the device, let's say we have a middleware or server that needs to authenticate users, the design may be each user might have different profiles, like a single person may have one id used on different devices like a phone tablet phablet etc, IMEI could be really handy to uniquely id the variant of the user thus avoiding errors and what not