Many thanks fly to Abhijit for having spotted a way to search for telephone numbers in Mozilla Thunderbird Address Book. You can read more on his blog at: http://ifacethoughts.net/2010/08/09/configuring-thunderbirds-addressbook-search

In short you need to access the config editor and look for the string:

mail.addr_book.quicksearchquery.format

the string content feature the 'attr' fields that are searched by the quick search bar (you may type 'attr' to see all the possible fields.

e.g. my string content is:

?(or(PrimaryEmail,c,@V)(DisplayName,c,@V)(FirstName,c,@V)(LastName,c,@V)(CellularNumber,c,@V)(HomePhone,c,@V)(Notes,c,@V)(PagerNumber,c,@V)(FaxNumber,c,@V)(WorkPhone,c,@V))

which searches the Primary Email, the Display Name, the Cellular Number, the Home Phone, etc...

Mozilla Thunderbird is such a powerful program! It's users are even more powerful though! :D