Merlin was the only other key system in its day with dual-color LEDs, aside from Panasonic. I'd venture to guess the Merlin LEDs were just a bit more visible under bright light. It was definitely a worthy competitor to Panasonic, unlike today's nasty Cisco phones where the Hold button is buried in contextual menus unless you pay a yearly fee for the feature pack that allows it to be on the first screen.
Touch-a-Matic had a role in a science fiction movie. I don't recall the title, but in this film, there was another Earth on the opposite side of the Sun, and we had an "exchange mission" to swap astronauts. Upon landing, the Earth 1 astronaut discovered that everything on Earth 2 was backward. In one scene he's at the house of his opposite number from Earth 2, having met his wife there, who is just like his wife here. Then he goes to make a phone call.
Touch-a-Matic. Backwards, with the handset on the right. Clearly done by using some kind of mirror on the camera while filming. I thought, oh that's clever, can't just use a regular wall phone because it would be symmetrical, but the handset on the wrong side makes it more clear that everything is backward.
I'd be interested in someone starting a topic on phones seen in film, particularly science fiction. And who can forget the videophone in _2001: Space Odyssey_?