[russell_w_b]

On 'traditional' dial telephones, there are two switches that operate when the handset is lifted. One set of contacts makes the loop by providing a low-impedance path between A and B lines by putting the induction coil, microphone and dial-pulse contacts (normally closed) in circuit. A relay at the exchange ('A'-relay?) detects the change-of-state and dialling tone is sent to the telephone.

The second set of contacts makes a spark-quench circuit by shunting the dial-pulse contacts (via a further dial contact called a 'dial off-normal' contact) with a CR circuit. This gives a clean dial pulse to signal to the exchange.

Both switches are lift-to-make on older (332) telephones, and are not changeover contacts. They operate simultaneously. More modern 700 series phones use a C/O contact on the spark-quench cct, but one set of contacts is strapped together. GPO instruments were made to be flexible and so this contact may have another use (of which I can't think of right now) dependent on its configuration.

I can't speak for anything more modern than an 8782 DTMF push-button instrument with bell, other than to say there's at least one switch for making the loop and seizing the line.