The purpose of the FOI act, is for public sector bodies to comply with requests for information that they hold.  The request for a geographic number, and the amount of money they earn from them, is quite a popular request from members of this site.  You can also ask for anything from minutes of council meetings, to who supplies the coffee for their vending machines!!

Commercial companies are not required to disclose information, however a public sector organisation such as the DVLA, or Inland revenue would only release the geo number because of pressure of the FOI act, and not of concern of customer relations.

A commercial organisation of course might take customer relations into account, and many do give a geo number at the request of a customer.  Whilst they do not have the FOI act to contend with, they do have to keep their customers happy.

Therefore in the spirit of customer goodwill, and commercial pressure, a company can give you their geo number, but there is no legal, or regulatory obligation to do so.

With regards to standard letters, they are generallya  waste of time. Far better to write your own bespoke letter.