circuit- or packet- switching does not happen inside the switch -- it happens on the network

Circuit or packet switching are fundamental paradigms in network stack design. Any switch there is only does one and not the other. The "switching" in packet switching is the individual forwarding of packetized data, which happens inside switches and routers (based on different network layers).

With circuit switching, the forwarding is done in bulk. A logical connection is established and the channel is allocated for the duration of that connection (when you're in a phone call the line is busy). Packets usually only carry labels and no complete source and destination addresses.

In packet switching, each packet must carry complete addresses and is forwarded on an individual basis. The forwarding network is essentially stateless and oblivious to any logical connections on higher network layers.

The difference in hardware is that circuit-switching hardware may only need to switch connections at a very low frequency (every few hours in extreme) while packet-switching hardware needs to switch at packet frequency (up to 1.4 million pps for a Gigabit Ethernet link).

An Ethernet switch uses one or more ASICs that are purpose-made. You cannot reprogram that hardware for another protocol.

circuit- or packet- switching does not happen inside the switch -- it happens on the network

Circuit or packet switching are fundamentally different paradigms in network stack design. Any switch there is only does one and not the other. The "switching" in packet switching is the individual forwarding of packetized data, which happens inside switches and routers (based on different network layers).

With circuit switching, the forwarding is done in bulk. A logical connection is established and the channel is allocated for the duration of that connection (when you're in a phone call the line is busy). Packets usually only carry labels and no complete source and destination addresses.

In packet switching, each packet must carry complete addresses and is forwarded on an individual basis. The forwarding network is essentially stateless and oblivious to any logical connections on higher network layers.

The difference in hardware is that circuit-switching hardware may only need to switch connections at a very low frequency (every few hours in extreme) while packet-switching hardware needs to switch at packet frequency (up to 1.4 million pps for a Gigabit Ethernet link).

An Ethernet switch uses one or more ASICs that are purpose-made. You cannot reprogram that hardware for another protocol.

However, if your "telephone switch" includes a switch used for VoIP then, of course, you can use (any) Ethernet switch as a "telephone switch".