Speed of PSTN?

Please clarify - since there are many different services provided on the PSTN, are you asking for the minimum speed available? Are you wondering about the "speed" of a modem on the PSTN? Keeping in mind that the PSTN is a combination of digital and analog links, talking about "speed" on the PSTN is not quite the same thing as talking about the speed of, say, an ethernet connection on a LAN.