if i have tel number,how to find out who used the number?any service for this case?

Answer 1

Do a reverse telephone search:
http://www.daplus.us

Answer 2

If you're in Singapore, which I think you are, none of the service providers will reveal such a confidential information to you (for mobile lines). Or, the subscriber of the line is not always the user of the line. For residential lines, there's always the yearly edition of the Yellow Pages. Good luck finding.
If that kind of information is readily available for mobile, how would you feel if someone can just go to SingTel and ask the service officer, "Eh you can tell me where this person who use number 98765432 live ah?"

Answer 3

You can dial 100 and try, but I doubt they will tell you, except in very unique cases where there is police involvement.

Answer 4

check out

http://goa.bsnl.co.in/dir_enq.htm

or

http://mumbai.mtnl.net.in/directory/individual.html

or search for local directory of particular place