Entryphone is a registered trademark, and may only be used with apparatus manufactured by this company.
The trademark provides protection for the name built up by considerable publicity and sales efforts continuously since 1958. The name must not be used in respect of other companies' products. The trade mark protects us for the word or words resembling the same, either visually or orally. Thus, splitting it into two, pluralising, or hyphenating would not avoid the infringement.