The "R" button...
Is a recall button, used when on a phone call to some one to bring back the dial to make another call which basically puts the other person on hold.
The Snoopy and Woodstock phone, as well as the Mikey Mouse phone, in the UK were suplied by British Telecom and made by the EET company for BT, in the very late 70s and early 80s, they were part of BTs TSR phones (Telephone Special Range) also named "Design line" by AT&T which these were part of in the US...Not sure what comapny made them in the US, but they were suplied by AT&T.
The only difference between the UK and US MM phone and the S&WS phone is the dial and internals.
The US one had a gold finish Western Electric 500 type dial, where as the UK one had a regular GPO type dial, the US one had a Trimline bell ringer, where as the UK ones had a Trimphone electronic ringer.
Also, both companies in both countries made them in push button varients as well as rotary dial...Although the UK push button model was pulse and not DTMF, like the US push button one, not sure why, I think many exchanges didn't supprt the digital tones back then, although the 782 phone, shown above, ^^ is DTMF and from around the same kind of time, so, who knows.
Here is the base of my BT Snoopy and Woodstock phone.
