Yes, a regular POTS line reads a nominal 48V DC (North America) or 50V DC (some other parts of the world), with ringing at approx. 90V AC. Ringing voltage can vary considerably though, and with some switching equipment close to the exchange it may rise over 100V.
In all modern systems the AC ringing is sumperimposed on the 48/50V DC, so that the ringing can be "tripped" and the call completed as soon as the phone is picked up (without the superimposed DC you'd have to wait for the next burst of ringing, which in the U.S. could be up to 4 seconds).
Other voltages can be found on lines from time to time however. As has been noted elsewhere, coin-phone lines sometimes used higher voltage DC pulses for coin collect/return, and maintenance routines will sometimes briefly connect higher voltages to the line for test purposes.
A typical modern DMM will be set on the 200V range for measuring tel. line voltages, and the built-in overload protection on most modern meters should easily cope with anything the line can throw at it (lightning strikes and direct shorts to HV power lines excepted!).
I'm not quite sure what you're getting at with taking resistance readings on a live line though.
If there's TelCo line current flowing,the meter reading will be meaningless. Or did you just mean would the meter be safe if you accidentally connected it to a live line?
Many modern DMMs will survive direct connection to the line on a resistance range, but a conventional analog meter might not do so well.
[This message has been edited by pauluk (edited 01-28-2003).]