Differentiating between different families of Executone telephones can be challenging, made especially difficult by the company's (shrewd) use of highly similar plastic casings for several major families of products.
The Executone Encore series of phones (not interchangeable and not to be confused with Encore CX) all have part numbers beginning with "251xxxx". The phones were originally manufactured in simple configurations wtih optional modules which would expand each desk set's functionality.
Hearkening back to the foundations of the company in the early 20th century when their primary product line consisted soley of "boss-to-secretary" closed intercom systems, the Encore phones may be seen with these once-optional speakerphone modules pre-installed.
If you are looking for a particular Executone Encore phone and can't find it listed here, please contact us and we will get back to you as quickly as possible with whatever help we can offer.