Rightly said by @Amrit they are unique and the telecom companies can identify the location based on IMEI , there are softwares used in telecom which can be accessible only to authorised personnel that show informations based on particular IMEI.
No there is no other number that can be used as unique for every mobile phones.
You can find your IMEI by typing *#06# in keypad.
You can find info about your mobile online : http://www.imei.info/
Hope that clears your question.