As a kid, this style was my favorite phone. While this particular model was updated with Redial and options for pulse dialing, I still enjoy the design. Even today, I love to see these in use as the ‘courtesy’ phone of choice for rental car locations, airports, etc. It stands the test of time.
From Wikipedia:
By the late 1960s interactive response systems in some industries required additional signaling beyond the ten digits. In 1968, the # key and the * key were added to the push-button dial pad, and the 2500-type telephone entered production. The additional keys were located on either side of the ‘0’ button to fill the matrix of 4-by-3 keys. These keys were initially unused by most customers, but would later be used for vertical service codes, and voice mail menu navigation. In 1974, when modular connectors were introduced, the 2500 telephone was fitted with modular connectors for the handset cord as well as the line cord, resulting in type designations suffixed with M, e.g. 2500DM. The 2500 is still commonly encountered today and it is still produced by several companies.
In addition to the basic single-line model, the Western Electric 2500-series included many related variations and special purpose models with additional features. This included sets with a headset jack, 2-line sets, keysets (2560), call directors, panel phones (2750), industrial phones (2520), automatic dialers (2660).[8]