Historically, the telephone battery voltage has been around 48 volts. Yes, they run the phones on batteries, which is why they ALWAYS work. Your home cordless phone or answering machine of course does not work without power, but any POT (plain old telephone) will always work.
More modern switchboards can be as low as 37 volts.
The ringing voltage can be anywhere between 40 and 90 volts.
In all cases, because of the amount of line resistance, the amount of current you could get through your body is not enough to hurt you, although if you put you fingers across the line just as it rang, you could get a tingle.