Flagging and/or Cleansing/Correcting bad telephone number data

Hoping that perhaps someone here has already been down this road and may be willing to provide some pointers.

Can anyone direct me to information regarding the use of PostgreSQL with other references to verify/flag bad telephone number data?

I've tables with 'people' data ( f/lname, addr, zip, telno, etc ). I know that some of the records have invalid telno's ( no area
code, transposed area code or transposed exchange digits, etc ) -- I'm looking for methods/means of identifying them, for example,
'..we've used Company X's product to validate area code and exchange against zipcode/state...', '...this contrib/addon should
help...', '..I used http://blah.blah.com as a reference for this...', '...using software/site/data provided by X you can automate
the lookup and validation of person/telno against person/telno in DB...', etc.

Please advise if there's a more appropriate forum for this also ( I realize that more appropriate may be more general than
PostgreSQL; at the same time I think this might be a position that many PostgreSQL users might find themselves facing so may be on
topic enough to warrant the email archives).

Thanks,
reid