On a fully time division multiplexed (read: no IP packets; just end-to-end multiplexed serial streams) call, it should be no more than ~40 milliseconds of latency from one side of the United States to the next, or no more than quantization delay from the g.711 codec (0.125 milliseconds) when simply traversing the bus of the local switch.

Thankfully, there's discounts stashed here and there for landline phones. Some are easier to get than others, though, and it definitely doesn't help that like with anything else from a telco, the price keeps getting jacked up.