Ideal makes an ABS (Almost Butt Set, no talk ability), that you can listen to the phone line without making connections (inductive pickup). You can also dial a test number to find out the number you are assigned through the provider, etc.

To use any phone line as a ... Phone, you'll need a butt set, very useful, but not cheap or extremely portable.

That's something I thought I wanted but couldn't justify the cost, so I never got one.

 

You will hear the dial tone if you connects e.g.your headset to the line too.

dsk